Skip to Content

Old-Fashioned Root Beer Float Cake with Creamy Root Beer Float Mousse Filling

Sharing is caring!




Summer isn’t over yet! Not even close! But it sure is flying by fast, is it for you, too? Wow! We had a nice break of cool weather there for a bit, but now it’s getting hot and humid again and we needed something to cool us off! This icebox-cold, creamy-dreamy, old-fashioned root beer float cake idea came out amazingly spectacular! And was the perfect Grand Finale to our Fried Chicken Dinner Week! I used 2 very old recipes, doctored them up a bit, and combined them all into one phenomenal double-layer cake with a fluffy “frosting” of Cool Whip! Both of these recipes were jotted down many years ago and I’m not sure of the original sources of either one. I’m pretty sure at least one of them came out of Taste of Home magazine, but I don’t know if the person who sent it in came up with it themselves. The second part was actually a pie recipe that said, in my own hand-writing, that it “didn’t set up well and had to be frozen overnight to get it sliceable”. So, if anyone knows the original sources of either of these, please let me know so I can provide an update and give proper credit! 

Ok, with all of that out of the way, I do believe I at least deserve an ounce or two of credit for making both taste a whole lot better and combining both parts into a dessert that you won’t soon forget! Ever! The first thing I need to tell you though, is that this is not a cake that would transport well. As a matter of fact, don’t even consider trying to make it further than the fridge to the table. Some things transport well, some things don’t. This does not. It also requires to be refrigerated at all times. Only remove cake to slice pieces and then refrigerate again to keep the filling and Cool Whip nice and chilled. Once pieces are sliced onto serving plates though, it can sit for awhile no problem. The cake just has to be quite cold to be able to slice properly is all.

So let’s get started! You’ll need to make the filling first so it can freeze. I took my time and did the whole filling/cake process in two days as to not rush anything and that worked out beautifully. I recommend that you do the same, although, if you made the filling early in the morning and the cake in the afternoon, you can probably squeeze it all in. *Both parts are very easy, but the filling does need to be frozen, and the cake completely cooled to be able to assemble. So just simply keep that in mind time-wise. Now, all we do for the filling is beat most of the ingredients on a low at first, then med-low speed so it doesn’t splatter, until it thickens a bit…



…then fold in the Cool Whip, gently, until all is incorporated. Easy right? I know!!! Then just spoon it into an 8″ cake pan lined with foil, sprayed, and pop into the freezer! I froze mine overnight. I wanted this to be as solid as possible, especially when trying to take photos at the same time! Then just lift it out from the pan holding on to the excess foil edges, and pop it back into the freezer to keep frozen until ready to assemble. Later, when the cake is made and cooled completely, you’ll just simply peel off the foil! *I had visions of picking ten thousand gazillion bits and pieces of tin foil from it if it stuck! But, nope, it peeled right off no trouble or sticking at all whatsoever. This will be your mousse filling layer in the middle…


Next is to mix up the cake batter and pour into 2 greased and floured 8″ cake pans…try not to lick the spoon and bowl too much…some of it does have to bake ya know! 😉 



Though a white cake is used, you’ll notice how beautifully rich the color is after baking due to adding all of the yummy ingredients! Simply gorgeous! The cakes have a nice rise, too! Not overly domed and perfectly done! (WHEW!)



Let them cool on a rack in the pans for about 15 minutes, then carefully turn out to cool completely…can you just smell them, too??…omg…heaven. Pure heaven… 



I always, right or wrong, cool my cakes top side-down on racks. And I like to assemble them that way, too. Then you have a nice surface to spread any sauces, fillings, frosting or mousses, etc., in both the middle and on top. I don’t know if this is correct or not, but it always works for me. Especially sauces and jams that need to “seep in”. And both crustier top-sides get softened from being against the plate on the bottom, and filling in the middle (bottom of second layer). So this is how I do it anyways. But I’m no pro!! You can assemble how ever you like, but for this especially, it worked perfectly. Now, we let them cool completely, and assemble with the frozen layer, and pop into the fridge…



I then left the cake in the fridge for awhile, about an hour or so, to let the mousse filling soften and go from frozen solid to creamy cold gently on it’s own. It was then nice and creamy “soft-serve ice cream soft”, but not runny, and I was able to spread it with the back of a spoon first to fill in the gaps between. I did then go around and scrape off the excess with an offset knife to make it all neat and purdy, but showing you this pic so you can see how lovely and creamy this filling is! The excess did not go to waste… 😉



Pop back into the fridge for a bit to refirm up edges a little, then “frost” with more Cool Whip! 



Chill to let everything set and make friends! Then get out the BIG knife! And some plates…uhm no, the bigger ones!! This cake is very light actually and a bigger piece can easily be handled. 😉 

Here’s a little peek inside…



And a slice just for you!!



And an important tip to slicing!!!




**Look at the inside RIGHT-hand cut (whole cake above) I did first when I went to cut the cake. I put the knife in the center, and lowered it and was cutting at an angle like I usually do, sawing back and forth a little and pressing downward a little with the knife semi-horizontal. Don’t do this. It will start to push the filling out a little bit. Now, look at the LEFT-side cut. I kept my knife STRAIGHT UP AND DOWN, and did an up and down sawing motion until I got all the way to the outside. Then came down at an angle through the frosting. That, as you can see, made all the difference and didn’t disturb the filling at all. Hope this tip helps to make this cake the most enjoyable experience! 

And this wraps up my “Homemade from Scratch Southern-Style Fried Chicken Dinner Week!” I hope you enjoyed it and found some go-to staples, new recipes to try, and a few to tuck away! 

Have a fantastic weekend all! Enjoy the last of the summer, because it’ll be snowing before we know it! And be sure to share a few slices with friends and neighbors! 😉 




10-12 servings


For Mousse Filling:

1 (4-serving size) package instant vanilla pudding mix

3/4 cup root beer

1/3 cup milk

1/4 tsp. vanilla

2 tsp. root beer concentrate, (*Walmart carries it)

1 (8 oz.) tub Regular Cool Whip, thawed in fridge


For Cake:

1 box Duncan Hines Signature French Vanilla cake mix

1 1/4 cups root beer

1/4 cup canola or vegetable oil

2 extra large eggs, room temp.

1 tsp. vanilla

1/2 tsp. root beer extract



1 (16 oz.) tub Cool Whip, thawed in fridge



Make mousse filling first:

Line an 8″ cake pan with foil well, with excess overhang, and spray inside lightly with cooking spray. Set aside. In mixing bowl, whisk on low to start, all mousse in ingredients except the Cool Whip. Bring speed up higher and whisk until it thickens a bit. About 3 minutes. (Scrape bottom and sides as necessary, about halfway through.) *You can choose to do this by hand if preferred but it will take longer. Fold in Cool Whip with a spatula until well combined.  Pour and spoon into prepared pan. Smooth and level surface with an offset knife or back of spoon. Pop into freezer and freeze until solid. At least 4 hours or overnight.  Remove from pan, lifting out, and with the foil intact place back into freezer.

For the cake:

Grease and lightly flour 2 – 8″ cake pans. Set aside. Preheat oven to instructions per pans that you are using. (350 or 325 degrees.) In large mixing bowl, add all ingredients and beat on low just until mixed. Then beat on medium speed for 2 minutes. Pour batter dividing evenly, into prepared pans, smooth and level batter. Bake according to instructions per box for 2 – 8″ cakes.

*I used dark-colored, non-stick pans, greased and lightly floured, and baked in a 325 oven for the full 36 minutes until it sprung back in the center when touched, was starting to pull away from the sides of the pans, and a toothpick inserted in the center came out clean.

Remove cakes to a wire rack for 15 minutes to cool slightly. Turn out onto rack to fully cool. 

When fully cool, place one layer onto serving plate. Remove mousse filling from freezer and remove foil. Place solid mousse directly onto bottom cake layer aligning with cake. Top with second cake layer. Refrigerate for at least an hour, or until mousse softens a bit on the edges. 

Take cake back out and smooth mousse filling to fill in gaps between cake and mousse layers. Use an offset knife or the back of a spoon. Chill until edges firm up.

Frost with Cool Whip and chill. 

Cut carefully keeping knife straight up and saw gently in an up and down motion working your way to the outside without pressing down against the cake and disturbing the mousse. 

Store in fridge!! *My lid to my cake plate wasn’t tall enough, so I stored mine uncovered but with a little piece of plastic wrap pressed up against the exposed cut part to keep the cake and filling moist. Did just fine. 











Print Friendly, PDF & Email