Chocolate mousse - very generous. Fudge topping - very thick. Chocolate cupcake - very dark. End result - sensational.

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

Make the cupcakes:
Put chocolate in heatproof bowl or the top of a double boiler and place it over, but not touching, a saucepan of barely simmering water or the bottom of the double boiler. Stir until chocolate is melted. Remove from the water and set aside.

Sift the flour, baking powder, baking soda, and salt into a medium bowl and set aside.. In a large bowl, using an electric mixer on medium speed, beat the butter and sugar until smoothly blended, about 2 minutes. Stop the mixer and scrape the sides of the bowl as needed. On low speed, mix in the melted chocolate. On medium speed, add the eggs one at a time, mixing until each is blended. Add the vanilla and beat until the mixture looks creamy, about 1 minute. Mix in the sour cream until no white streaks remain. On low speed, add half of the flour mixture, mixing just to incorporate it. Mix in the water. Mix in the remaining flour mixture until it is incorporated and the batter looks smooth.

Fill each liner with a generous 1/3 cup of batter to just below the top of the liner. Bake 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. Remove the cupcakes from the pan onto a wire rack and let cool completely.

Make the topping:
In a medium saucepan, heat the cream and butter over low heat until cream is hot and butter has melted. The mixture should form tiny bubbles and measure about 175°F on a thermometer; do not let it boil. Remove the pan from the beat, add the chocolate chips, and let them sit in the hot cream for about 30 seconds to soften. Add the vanilla and whisk until it is smooth and all the chocolate has melted.

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. Spread 1 tablespoon of the chocolate topping over each top. Let sit until the topping is firm.

Make the filling:
Put the remaining chocolate fudge topping in a large bowl. In a separate 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 Fudge Topping until no white streaks remain. Use a rubber spatula to fold in the remaining whipped cream. Using an ice cream scoop with a 1/4-cup capacity, place a scoop of mousse on each cupcake bottom. Using a wide spatula, carefully place the cupcake tops on top of the mousse. Refrigerate to firm the chocolate topping, then cover and keep refrigerated. Serve cold.