Make the cupcakes. Position a rack in the middle of the oven. Preheat the oven to 350°F. Line 12 muffin tin cups with paper cupcake liners.

Fill each liner with a generous 1/3 cup of batter (about 6 tablespoons), to just below the top of the liner. Bake just until the tops feel firm and a toothpick inserted in the center comes out clean, about 20 minutes. Cool the cupcakes for 10 minutes in the pan on a wire rack.

Use a small knife to loosen any tops that might have stuck to the top of the pan. Carefully place the wire rack on top of the cupcakes in their pan. Protecting your hands with pot holders and holding the pan and rack together, invert them to release the cupcakes onto the wire rack. Turn the cupcakes top side up to cool completely.

Frost the cupcakes. Use a sharp knife to slice the top (about a 3/8-inch-thick slice) off each cupcake, and place the tops right side up on a wire rack. Place the cupcake bottoms on a serving platter; set aside. Spread 1 tablespoon of the warm chocolate sauce over each top. Let sit until the sauce is firm.

Make the filling. Put the chocolate sauce in a large bowl; set aside. In a large bowl, using an electric mixer on low speed, beat the cream, powdered sugar, and coffee granules until the coffee dissolves, about 1 minute. Beat on medium-high speed until firm peaks form. Whisk about 1 cup of the whipped cream into the chocolate sauce until no white streaks remain. Use a rubber spatula to fold in the remaining whipped cream. Using an ice cream scoop with a ¼-Cup capacity (which works best to form a smooth edge) or a large spoon, place a scoop of mousse on each cupcake bottom. Using a wide metal spatula, carefully place the cupcake tops on top of the mousse. Refrigerate to firm the chocolate topping, then cover and keep refrigerated. Serve cold.

The cupcakes can be refrigerated for up to 2 days.