Preheat the oven to 350 F. Butter and flour a 12-inch round cake pan or your muffin pans.
To Make the Cake: Combine the flour, baking powder, and salt in a medium bowl; set aside.
In a separate large bowl, cream the butter and sugar with a mixer until fluffy.
Add the eggs one at a time, beating after each addition.
Stir in the vanilla. Add the flour mixture to the butter mixture, alternation with the sour cream, and mix until blended.
To bake: Pour batter into the prepared pan and bake for 25-30 minutes, or until a knife inserted in the center comes out clean. Let cool in the pan.
To make the Tres Leches Topping: Stir together the milk, condensed milk, and evaporated milk. when the cake is cool, remove from the pan and transfer to an ovenproof serving tray. Pierce the cupcakes (or cake) all over with a fork.
Spoon the milk mixture over the cake and let soak for 5 minutes. (I let mine soak for about 15-20 minutes). I brushed it on my cupcakes with a pastry brush. I didn’t use all the tres leches mixture on the cupcakes.
Whipped Cream: Whip one pint of heavy cream until soft peaks form. Don't overbeat it because you will then have butter:)Add two tablespoons of powdered sugar and combine for about 1 more minute.
For Cake or Cupcakes: Pipe or spoon on the whipped topping. Don’t forget the cherry on top!