For the pink champagne cake: Preheat the oven to 350 degrees F. Lightly coat three 8-inch cake pans with cooking spray.
Whisk together the all-purpose flour, cake flour, baking powder and salt in a medium mixing bowl. Set aside.
Combine the granulated sugar and butter in a large bowl and beat with an electric mixer until light and fluffy, about 3 minutes. With the mixer on low, add one-third of the flour mixture to the creamed butter mixture. Mix until the flour is just blended. Combine the Champagne and milk. Beat in half of the Champagne mixture. Alternate adding the flour mixture and the Champagne mixture, ending with flour and incorporating fully. Set aside.
Beat the egg whites with an electric mixer just until foamy. Add the cream of tartar and beat until stiff peaks form. Gently fold one-quarter of the egg whites into the batter. Then fold in the remaining egg whites.
Spoon the batter into the prepared cake pans. Bake until a toothpick inserted into the center comes out clean, 30 to 35 minutes. Cool the cakes in the pans on a wire rack for 10 minutes, then remove from the pans and cool completely.
For the stabilized whipped cream: Pour the heavy cream into a medium bowl. Add the powdered milk, vanilla and 6 tablespoons of the confectioners' sugar. With an electric mixer, beat the cream until it reaches stiff peaks, adding additional confectioners' sugar if needed for desired consistency. (Makes 2 cups.)
For the strawberry Swiss meringue buttercream: Place a glass bowl over a saucepan filled with approximately 1 inch of water; bring to a simmer. Add the egg whites and granulated sugar to the bowl. Cook, whisking constantly, until the egg whites are hot, the sugar is dissolved and the temperature of the mixture has reached about 140 degrees F. (You can test this by rubbing a small amount between your fingers to make sure it's not gritty.)
Pour the hot egg mixture into the bowl of a stand mixer. Beat with the whisk attachment until the bottom of the bowl is no longer warm and the meringue is thick and glossy, 7 to 10 minutes.
Slowly add the butter cubes, one at a time, until incorporated. The mixture may curdle; keep beating and it will come back together. Continue beating until the mixture is silky and smooth. If it becomes too thin, refrigerate for around 15 minutes and then beat until it comes together.
Add the pureed strawberries, vanilla extract, salt and a splash of lemon juice. Mix until smooth. (Makes 5 cups.)
To assemble the cake: Fold the diced strawberries into the stabilized whipped cream, then spread half of the strawberry whipped cream on the top of one cake layer. Place a second cake layer on top of the filling. Repeat with the remaining half of the whipped cream. Place the third cake layer on top of the second. Frost the entire cake, top and sides, with the strawberry Swiss meringue buttercream.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.