Simmer 2 cups of whole milk with 1 teaspoon of vanilla extract in a saucepan over medium heat. In a separate bowl, whisk together 3 large egg yolks, ⅓ cup granulated sugar, and 2 tablespoons of cornstarch until smooth. Gradually add the hot milk to the yolk mixture, return everything to the saucepan, and cook over low heat until thickened for 5-7 minutes. Refrigerate until cool.

Preheat oven to 350°F (175°C) and line a 9-inch round cake pan with parchment. In a mixing bowl, whip 4 large eggs and ⅓ cup granulated sugar until pale and fluffy for about 5-7 minutes. Gently fold in 1 cup sifted all-purpose flour and 2 teaspoons of baking powder. Pour the batter and bake for 25-30 minutes.

Prepare the strawberry syrup by simmering 1 cup of chopped strawberries, ½ cup water, and ½ cup granulated sugar for about 10 minutes. Strain through a sieve and let the syrup cool.

Carefully slice the cooled genoise sponge in half horizontally. Soak one layer with strawberry syrup, place sliced strawberries around the edge, and pipe diplomat cream in the center. Alternate layers with more strawberries and top with the second genoise layer soaked in syrup.

Cover the cake with plastic wrap and refrigerate for at least 4-5 hours before serving. Remove the cake ring and slice into wedges.