Buttercream Fruit Mousse Filling and Frosting

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Cake and photo by Sarah Phillips © Sarah Phillips

SARAH SAYS: "For an Easter dessert, I was on my way to making the "I Heart Strawberries" Cupcakes, when I discovered I did not have enough strawberries to make both the Strawberry Ultimate Butter Cake cupcakes AND the filling. So, I quickly changed course, and made a Citrus Ultimate Butter Cake, and developed a luscious buttercream berry filling and frosting to go along with it! My guest list also increased in size, and I no longer had time to fill cupcakes, so I decided to make a layer cake, instead, which is faster to assemble!

I baked a two layer Ultimate Butter Cake or UBC and flavored it with 3 tablespoons finely grated lemon peel, 2 tablespoons finely grated orange peel, and flavored the cake with 1 tablespoon vanilla extract.

I used a version of Tami’s or Perfect Buttercream, and wondered what would happen if I made a strawberry puree, and then, beat it into the buttercream? Strawberry flavor is the hardest to impart in a recipe because the flavor is not intense and can be lost easily. I always like to use fruit purees because they lend the freshest flavor, but you need a lot of it, and in turn, they can water down or ruin a buttercream recipe - basically because butter and water (or buttercream and fruit) do not mix easily! Most recipes have you simply add in a fruit puree directly to the recipe, which I find, causes it to break down easily.

I do not recall a recipe anywhere where fruit purees are successfully added to buttercream and the buttercream remains stable! This is the first! This one works. Find out how I did it."

imsyigg, Premium Member, Says: "I know I can always count on you, Sarah...."


The resulting buttercream, which I made with all butter, is really fluffy and light, and the added strawberries, first cooked with cornstarch, helped make the whole recipe taste almost like a mousse. The flavor is intense and I suppose one can make any cornstarch-fruit base, such as boysenberries or raspberries or even peaches, to add to the buttecream, thus, yielding lots of fresh fruit flavors! The buttercream was also very stiff /stable because of the cooked cornstarch and fruit mixture."

1 1/4 cups whole strawberries; makes 2/3 cups pureed strawberries
2 - 4 tablespoons of granulated sugar; depending on the sweetness of your berries
1 tablespoon cornstarch
1/4 cup COLD water
2 to 4 tablespoons strawberry syrup; such as Hershey's; optional

For 2 9 x 2-inch layers or 24 cupcake (Makes 3 cups):

1 1/4 cups (2 1/2 sticks) unsalted butter, cold
2 tablespoons (1/8 cup) to 4 tablespoons (1/4 cup) heavy whipping cream or milk
2 teaspoons vanilla extract
4 to 5 cups (over 1 pound) powdered sugar, sifted; measure than sift
1/2 teaspoon salt

1. Puree whole strawberries in the food processor.

Measure 2/3 cup of strawberry puree, to use in the filling, and pour that into a small saucepan.

2. Heat mixture, over medium heat, stirring, and add sugar. Taste after first two tablespoons of sugar are added, to make sure it is sweet enough, before adding more.

3. Make the cornstarch mixture:
A. Place water in a small cup.

B. Add the cornstarch and stir to combine.

4. When the strawberry mixture comes to a low boil, slowly add the cornstarch mixture, stirring constantly, so you don't get lumps.

5. Gently boil mixture for about one minute, stirring. It should be thickened and no longer look opaque. 

Stir in the strawberry syrup.
Pour filling into a bowl and place plastic wrap directly on the surface, so a skin does not form. Place in refrigerator to cool.

1. In your mixer bowl fitted with a paddle attachment, beat the butter until smooth and light and fluffy, but not melted and greasy.

2. Add in the smaller amount of the heavy cream indicated in the recipe and the vanilla and mix well.

3. With the mixer on low, add in half the powdered sugar and mix on medium-low for 5 minutes. Add remaining sugar and mix well.

1. Add in the cooled and cooked strawberry puree in two portions, beating on medium after each addition. After both have been added, continue to beat the mixture on medium-high or gih for about 2 minutes, until the buttecream becomes light and fluffy.

2. Stop the mixer during the 2 minutes, and look at the buttercream. If it looks glossy and "wet", add in 1/4 cup powdered sugar and beat, again. Repeat until the frosting is thick, fluffy and no longer looks glossy.

Because the frosting contains fresh fruit, refrigerate it. But, it will become stiffer than when first prepared because of the butter and cornstarch in it. Let sit to room temperature to warm and refluff with a wire whisk.

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