Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
Sift flour and baking powder together and set aside.
Cream butter and 1 cup sugar together until fluffy. Add egg yolks one at a time, beating well after each addition.
Stir in 1/2 teaspoon vanilla extract. Add flour mixture to the batter, alternating with 1/2 cup of heavy cream. Mix until just combined.
In a separate bowl, beat egg whites on high speed until soft peaks form. Gradually add the remaining sugar, and continue to beat until stiff peaks form. Fold egg whites into the batter gently.
Pour batter into the prepared pan and spread evenly. Bake in preheated oven for 30 minutes. Check cake is done by inserting a toothpick in the center; it should come out clean.
Combine the evaporated milk, condensed milk, and 1 cup heavy cream. Pour this mixture over the warm cake until it is absorbed.
To make the topping, whip 1 1/2 cups heavy cream with 1 cup sugar and 1 teaspoon vanilla extract until thick.
Spread over the cake and refrigerate for at least an hour before serving. Enjoy your Tres Leches Cake!