Preheat the oven to 325 degrees F. Line two standard muffin pans with 20 cupcake liners.
For the cupcakes: Put 1/2 cup of the granulated sugar, the egg whites and whole egg in the bowl of a stand mixer fitted with a paddle attachment and beat on medium-high speed for about 2 minutes. Pour into another bowl and set aside. Clean the mixing bowl. Put the remaining 1 cup sugar and the butter in the clean mixing bowl and beat on medium-high for about 30 seconds. Add the flour, milk, sour cream, baking powder and vanilla. Beat on medium until combined and fairly smooth. Return the egg mixture to the mixing bowl and stir just until incorporated. Using a 1/4-cup ice cream scoop, fill each cupcake liner with batter.
Bake the cupcakes until a cake tester inserted in the center comes out clean and the tops are light golden brown, 17 to 20 minutes. Transfer the pans to cooling racks and cool for about 10 minutes, and then transfer the cupcakes to the racks and allow to cool completely before filling and frosting.
For the quatro leches mixture: Whisk the coconut milk, sweetened condensed milk, evaporated milk and heavy cream in a mixing bowl to combine. Transfer to a squeeze bottle and refrigerate.
When the cupcakes are cool, make the frosting: Combine the cream, powdered sugar and vanilla in a chilled mixing bowl. Whip until medium-stiff peaks form. Be careful not to over whip. Chill briefly if not using right away.
To assemble: Use a chopstick or fat skewer to poke 4 or 5 holes halfway through each cupcake. Squeeze some of the quatro leches mixture into each hole; you can let it sink in a bit and then squeeze in some more to fill. Frost generously with the whipped cream frosting.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.