Preheat oven to 350°F (175°C). Grease a 9×13-inch pan.
Beat egg whites until soft peaks form. Gradually add 1 cup sugar and beat until stiff peaks form. Set aside.
In another bowl, beat egg yolks with remaining 1 cup sugar and softened butter until pale and creamy.
Mix in vanilla, flour, baking powder, and salt. Add milk and mix until smooth.
Fold in egg whites gently until fully combined.
Pour into pan and bake for 30 minutes or until a toothpick comes out clean.
Let cake cool for 10 minutes. Poke holes all over with a fork.
Whisk together the leches and pour evenly over the cake. Chill for at least 3 hours or overnight.
Make whipped topping: Beat heavy cream, powdered sugar, and vanilla until stiff.
Spread whipped cream over chilled cake and sprinkle cinnamon if using.