Preheat oven to 350°F (175°C). Grease and flour three 9-inch round cake pans.
Whip eggs whites until they form medium peaks. Set aside.
Combine sifted flour and baking powder. Set aside.
Whisk together milk, strawberry puree, lemon zest, and vanilla. Set aside.
In a large mixing bowl, cream together butter, sugar, dry strawberry Jell-O®, and salt. Beat in eggs yolks one at a time.
Stir flour mixture into batter alternately with strawberry-milk mixture.
Gently fold in whipped egg whites.
Pour batter evenly into the three prepared cake pans. Bake in preheated oven for 20-25 minutes, or until a toothpick or skewer comes out clean.
Allow cakes to cool in their pans over wire rack for at least 10 minutes. Carefully tap out onto wire rack to cool completely.