The filling mixture usually takes about 15 minutes to boil; after that, it will thicken enough to use in the cupcakes.
I used toasted coconut as a light garnish on top of the frosting. It made it more obvious that the cupcakes were German Chocolate (since you can't see the filling) and added some nice color and texture to the cupcake.
I've seen many German Chocolate cupcake recipes call for what I used as filling as the primary frosting. I haven't tried that because I know how dense the German Chocolate filling is and don't want my cupcakes to topple over from the weight of the frosting. Besides, you can't really go wrong with filled cupcakes.
GERMAN CHOCOLATE CUPCAKES
1 box German Chocolate cake mix
4 large eggs
1 cup sour cream
1/2 cup milk
1 tablespoon vanilla extract
1/4 teaspoon salt
1 cup evaporated milk
1 cup sugar
3 egg yolks, lightly beaten
1/2 cup butter
1 1/2 teaspoon vanilla extract
1 1/2 cups chopped pecans
1 1/2 cups shredded coconut
1 cup plus 2 tablespoons granulated sugar
1/4 cup water
1/4 cup heavy cream
12 ounces (3 sticks) unsalted butter, softened
4 large egg whites, room temperature
1 teaspoon pure vanilla extract
Preheat oven to 350F.
Line cupcake pan.
Combine all ingredients in stand mixer and beat until combined.
Fill cupcake liners 2/3 full.
Bake 18-22 minutes (until toothpick comes out clean).
Remove from oven and transfer cupcakes to wire rack to cool.
In medium sauce pan, combine evaporated milk, sugar, egg yolks, and butter. Stir constantly over medium heat until thickened. Stir in vanilla extract, pecans, and coconut. Let cool.
Cut or core out center of each cupcake, discarding removed cake. Fill cupcakes with the pecan filling and refrigerate cupcakes about 20 minutes to cool.
Bring 1/2 cup plus 2 tablespoons sugar and the water to a boil in a medium saucepan. Wash sides of pan with a wet pastry brush to prevent sugar crystals from forming. Cook, undisturbed, until caramel is dark amber. Remove from heat, and slowly add cream, stirring with a wooden spoon until smooth. Let cool.
Beat butter with a mixer on medium speed until pale and fluffy, about 3 minutes. Transfer to a large bowl.
Place whites and remaining 1/2 cup sugar in a heatproof mixer bowl set over a pot of simmering water. Whisk until sugar dissolves and mixture registers 160 degrees on a candy thermometer.
Remove from heat, and attach bowl to a mixer. Whisk on medium speed for 5 minutes. Increase speed to medium-high, and whisk until stiff, glossy peaks form, about 6 minutes. Reduce speed to medium, and add beaten butter, cup at a time, whisking well after each addition. Whisk in vanilla.
Switch to paddle attachment. With mixer on low speed, add caramel, and beat until smooth, 3-5 minutes.