Step 1Heat the oven to 350 degrees. Spray 2 (8-inch) round cake pans with cooking spray, then line the bottoms of the pans with parchment paper and spray again. Set aside.
Step 2Beat the egg whites until foamy, then add the cream of tartar. Beat again until stiff peaks form. Gradually beat in three-fourths cup sugar and then set aside.
Step 3In a separate bowl, beat the egg yolks with the remaining three-fourths cup sugar until they form a thick yellow-colored ribbon. Stir in the water and the vanilla.
Step 4Sift the flour and the baking powder twice. Gradually fold the flour mixture into the egg yolk mixture by hand, until thoroughly combined.
Step 5Fold the egg white mixture into the flour and egg yolk mixture.
Step 6Pour the combined mixture into the prepared cake pans and bake until a wooden pick inserted in the center comes out dry, about 30 to 40 minutes. Let the cakes cool.
Step 7Cut each cake into 2 layers.
Step 8Whip the cream. Gently stir in the powdered sugar. Set aside 1 1/2 cups of the whipped cream to spread around the sides of the cake.
Step 9In a bowl, crush half the berries. Add the remaining whole berries. Gently fold the berries into the remaining whipped cream.
Step 10Spread one-fourth of the berry whipped cream over the bottom cake layer. Top with a second layer of cake. Repeat with the remaining two layers, and spread the last one-fourth of the berry whipped cream on the top of the cake. Frost the sides of the cake with the reserved plain whipped cream. Serve immediately or refrigerate until serving time.