Preheat oven to 350° F. Grease a 9 by 13-inch pan and set aside.
In a large bowl, add egg whites and beat until foamy. Slowly add ¼ cup granulated sugar and continue beating until stiff, but not dry, peaks form (when removing the whisk, the egg whites will stand straight up and form a "peak.") Transfer the egg whites to a smaller bowl and set aside briefly.
In the same large bowl, add egg yolks and the rest of the sugar (¾ cup) and beat on high until light yellow in color and thick. Add milk and vanilla on low speed until well combined.
Carefully fold in egg whites until no more streaks of egg whites are seen. Sift flour, baking powder, and salt over batter and fold into batter gently and completely.
Pour into prepared pan and bake for 30-35 minutes, or until cake springs back when lightly touched, and a toothpick inserted into the center comes out clean. Cool completely on a wire rack.
Mix the Milk Mixture
Using the blunt end of a wooden skewer (or anything that will poke small holes), poke several holes into the cake.
In a medium bowl, whisk together the three milks. Pour the milks over the cake. Cover the cake and refrigerate for at least six hours, preferably overnight.
In a large bowl, begin whipping heavy cream until thickened. Add powdered sugar and vanilla and continue whipping until stiff peaks form. Spread over soaked cake and top with strawberry slices. Slice and serve.