German Chocolate Cupcakes

Ingredients

• 2 ounces (60 g) bittersweet or semisweet chocolate, chopped
• 1/4 cup (60 ml) boiling water or coffee
• 8 tablespoons (4 ounces, 115 g) unsalted butter, at room temperature
• 3/4 cup (150 g) sugar
• 2 large eggs, at room temperature, separated
• 1/2 teaspoon vanilla extract
• 1 cup plus 1 tablespoon (150 g) cake flour (not self-rising)
• 1 tablespoon unsweetened natural cocoa powder
• 1/2 teaspoon baking soda
• 1/2 teaspoon salt
• 1/2 cup (125 ml) buttermilk (see note), at room temperature
• 3/4 cup (180 ml) evaporated milk (whole milk)
• 1/4 cup (60 g) packed light brown sugar
• 2 large egg yolks
• pinch of salt
• 2 tablespoons (30 g) butter, salted or unsalted, at room temperature
• 2 ounces (55 g) bittersweet or semisweet chocolate, chopped
• 1 1/2 cups (110 g) sweetened or unsweetened coconut flakes, lightly toasted
• 1 cup (125 g) chopped, toasted pecans
• 1/2 teaspoon vanilla extract