CUPCAKES:Heat oven to 350°F. Line cupcake tin with grease-proof paper liners such as foil ones. It will be important to get good quality grease-proof liners so the milk doesn't soak through the papers. Cream butter and sugar in stand mixer until light and fluffy on medium speed, a few minutes. Add egg yolks one at a time. Add vanilla. Combine flour, baking soda, and salt. Alternately, add the dry mixture and the buttermilk to the butter mixture, beginning and ending with flour. In a small glass or metal bowl, beat the egg whites on high speed until stiff peaks form. Fold egg whites into cake batter. Fill paper-lined wells 1/2 to 3/4 of the way full. Bake for 10 to 15 minutes or until toothpick inserted in center comes out clean. Let cool in tin for 10 minutes. Transfer cupcakes to cookie sheet. Stir together the evaporated milk, sweetened condensed milk, and the coconut milk. Poke about 7 holes in the top of the cupcakes with a toothpick. Pour 1 tablespoon of the milk mixture over each cupcake while they are still warm. Refrigerate for 2 hours or overnight before frosting. DULCE DE LECHE FROSTING:Cream butter and shortening together until smooth and no lumps. Add in vanilla extract, salt, and powdered sugar a little at a time. Add the dulce de leche a little at a time until desired flavor achieved, then add cream as needed to make frosting smooth and the right consistency for piping. The dulce de leche will thin the frosting out a little so add that before the cream. DULCE DE LECHE:Take a can of sweetened condensed milk, remove the paper label, and boil it in water for 3 hours. You can use a slow-cooker. Make sure the can stays completely covered in water the whole time. After 3 hours, you will poke into it and it will ooze a golden delicious caramelized liquid. SERVE:Use a round tip to frost the cupcakes with the dulce de leche frosting. Drizzle the dulce de leche on top of the cupcakes.