Step 1

Preheat oven to 350°. Grease two 8" cake pans with cooking spray then line with parchment rounds.

Step 2

Make cake: In a medium bowl, whisk together flour, cornstarch, baking powder, and salt. In another medium bowl, whisk to combine egg whites, champagne, and vanilla.

Step 3

In a large bowl using a hand mixer, cream together sugar and butter until light and fluffy, 2 to 3 minutes. Alternate adding the flour mixture and the egg mixture, beginning and ending with the flour mixture. Fold in lemon zest and divide batter between prepared cake pans. Bake until sides of cakes begin to peel away from baking pans, about 30 minutes. Let cool for 30 minutes, then turn out onto a cooling rack to cool completely.

Step 4

Make frosting: In a large bowl using a hand mixer, combine powdered sugar, butter, sour cream, vanilla, and salt until smooth. Reserve 1 cup frosting in a medium bowl and gently fold in chopped strawberries to combine.

Step 5

Place one layer on cake stand or serving platter, then top with the strawberry frosting and second cake layer. Frost top and sides of cake, then transfer remaining frosting into a piping bag fitted with a star tip. Pipe dollops of frosting all along the outside of the cake. Sprinkle with clear sanding sugar and serve.