Preheat oven to 350ºF. Grease and flour a 9x13 inch baking pan. Sift flour and baking powder together and set aside. Cream the butter and 1 cup of the sugar together until fluffy. Add the eggs and ½ teaspoon of the vanilla. Beat well. Add the flour mixture to the butter mixture, 2 table spoons at a time mixing well until blended. Pour batter into prepared pan. Bake for 30 minutes.
When cake has finished baking, pierce it in 8 or 10 places with a for or skewer, and let it cool. Combine the whole milk, evaporated milk, condensed milk and liqueur and pour over the top of the cooled cake. Refrigerate for at least 2 hours before serving.
Whipped Cream topping: When ready to serve, combine the whipping cream and the remaining 1 teaspoon of vanilla and 1 cup of sugar, whipping until thick. Spread over top of cake.
Because of the milk in the cake it is very important that you keep the cake refrigerated until ready to serve. Serve chilled.