This Mixed Berry Sheet Cake with Whipped Mascarpone Frosting has a spongy vanilla cake studded with fresh berries and is topped with a light and airy whipped mascarpone frosting.

Slice of mixed berry sheet cake with whipped mascarpone frosting and topped with strawberries and blueberries.

Between the moist crumb, creamy whipped topping, and pops of fresh fruit, this cake manages to be both light and satisfying.

Key Ingredients

Cake Flour – Cake flour contains less protein than all-purpose flour, resulting in a moister and fluffier cake that makes it worth having this ingredient on hand. Cake flour is made by combining flour and starch, often corn starch. It can be found in most grocery stores. If you want to make it yourself, simply measure out 1 cup of all-purpose flour, remove 2 tablespoons of flour and replace it with 2 tablespoons of cornstarch. Stir well to combine.

Dairy & Eggs – Make sure that your milk, sour cream, and egg whites have a chance to come up to room temperature before you begin mixing everything together. Allowing these ingredients to come to room temperature makes for a smoother batter. And, of course, be sure to allow the butter to soften before combining it with the sugar.

Mixed Berries – In this version, I used strawberries and blueberries but you can use whatever berries you like. Raspberries and blackberries would be delicious! You’ll notice that I cut the strawberries to be about the same size as the blueberries, which I left whole. Making the berries roughly the same size will provide more consistency throughout the cake.

Mascarpone Cheese – This addition to the whipped frosting not only lends to a more rounded flavor but also helps to stabilize the frosting. Often, whipped topping will fall and start to melt fairly quickly. By adding mascarpone cheese to the mix, the frosting maintains its structure.

Step By Step Instructions

Step 1:

Preheat the oven to 350°F and prepare an 11x15x2 cake pan by greasing it with butter.

Step 2:

In a bowl, combine the flour, baking powder, and salt.

Step 3:

In a large liquid measuring cup, measure the milk. Then stir in the sour cream, egg yolks, and vanilla.

Step 4:

In a large bowl, with an electric hand mixer, cream together the sugar and softened butter. Make sure they are well incorporated, mixing for about 2 minutes.

Step 5:

Begin by adding 1/3 of the flour mixture to the butter mixture, whisking only until just combined.

Then, add half of the milk mixture.

Continue with another 1/3 of the flour.

Then, the other half of the milk.

And finally, finish with the last 1/3 of flour, stirring just until combined.

Step 6:

Bowl of cake batter with mixed berries ready to stir in

To the berries, add about 1 tablespoon of cake flour and toss to coat. Then, gently fold the berries into the batter.

Step 7:

Transfer the batter to the prepared cake pan and smooth out the top.

Step 8:

Bake for 35 to 40 minutes, until a toothpick comes out clean and the top is very lightly golden.

Allow the cake to cool for at least 2 hours before frosting.

Step 9:

Once the cake is completely cool, prepare the frosting by creaming together the heavy cream, mascarpone cheese, powdered sugar, and vanilla until it is a smooth whipped consistency and stiff peaks have begun to form.

Step 10:

Spread the whipped topping over the cake. I used some of the blueberries and strawberries to make a 4th of July flag cake, but you can decorate however you like!