Tres Leches Cupcakes with Dulce de Leche Buttercream

Can you believe that I'm posting a dessert that isn't chocolate? What is that about? Well, it's a fabulous dessert! These dainty cakes are sweet and moist, and the buttercream is caramel perfection.
Tres Leches
1/4 cup shortening
1/2 cup unsalted butter, softened
1 cup sugar
3 eggs, separated
1/2 teaspoon vanilla extract
1 cup all-purpose flour
1/2 teaspoon baking soda
1/2 teaspoon salt
3/4 cup buttermilk
1/2 cup evaporated milk
1/2 cup sweetened condensed milk
1/2 cup coconut milk

In a large mixing bowl, cream shortening, butter, and sugar. Add egg yolks 1 at a time. Add the vanilla. Sift together the flour, baking soda, and salt. Add alternately with the buttermilk to the creamed mixture. In a small bowl, beat the egg whites on high until stiff peaks form. Fold into the cake batter. Fill muffin tins 3/4 full. Bake for 20-25 minutes. Let cool in pan for 10 minutes. While cupcakes are still warm, stir together the three milks. Poke holes into the cakes and pour milk mixture over each cupcake, filling each hole. Refrigerate for at least 2 hours. Remove from pans.

Buttercream
1 can sweetened condensed milk
2 egg yolks
3/4 cup sugar
3 tablespoons cornstarch
1/4 teaspoon salt
1/4 cup water
1 teaspoon vanilla extract
14 tablespoons unsalted butter, softened to room temperature
1 cup powdered sugar

For the buttercream: Pour the sweetened condensed milk into a glass pie plate and cover with foil. Place in a larger roasting pan and fill the pan with hot water, to a depth of about halfway of the pie plate. Place in the oven and bake at 425 for 1 hour 15 minutes. Remove from the oven and let cool. Stir until smooth.

Place the egg yolks in a medium mixing bowl. Stir the sugar, cornstarch, and salt together in a small, heavy saucepan. Whisk in the water first, then the dulce de leche and bring to a boil over medium heat. Boil for 1 minute, whisking constantly. Remove from heat. Gradually whisk the dulce de leche mixture into the 2 egg yolks. Stir in the vanilla. Strain through a wire mesh strainer into a small bowl. Cool completely.

Beat the butter on high until light and fluffy. Beat in the cooled dulce de leche mixture. Beat in the 1 cup powdered sugar until smooth. Frost cupcakes liberally.