For the devil's food cake:
Preheat oven to 350 degrees F. Coat the bottom and sides of a 9- by 13-inch metal baking dish with cooking spray (I like Baker's Joy) and line with parchment paper. Lightly spray the paper.
Combine the chocolate chips, cocoa and espresso powder in a mixing bowl. Pour the boiling water over top and whisk until the chocolate is completely melted. Set aside.
In another bowl, add the flour, baking soda, baking powder and salt and whisk to combine. Set aside.
In the bowl of a stand mixer fitted with the beater blade, cream together the butter and sugar on medium to medium-high speed until light and fluffy, 4 to 5 minutes. Add the eggs, one at a time, until incorporated. Whisk the buttermilk and vanilla into the reserved chocolate mixture. Reduce speed to low. Add 1/3 of the flour mixture, followed by 1/2 of the chocolate mixture until just combined. Repeat with another third of flour, the remaining chocolate, and final third of flour.
Pour the batter into the prepared baking dish and smooth with a rubber or offset spatula. Bake for 28 to 32 minutes, until a toothpick pricked in center comes out clean. Cool the pan on a wire rack for 10 minutes. Run a paring knife along the edges of the cake and gently invert it onto the cooling rack. Discard the parchment paper and allow the cake to cool completely.
For the mocha mousse:
Melt the butter in a medium saucepan over low to medium-low heat. Add the chocolate chips and espresso powder, and cook until chocolate is completely melted. Pour in the condensed milk and coffee liqueur and whisk until smooth and creamy, about 2 minutes. Set aside to cool.
In the bowl of a stand mixer fitted with the whisk attachment (or with an electric mixer) beat the cream until stiff peaks begin to form. Gently fold cooled chocolate mixture into the whipped cream until it is completely incorporated and no streaks remain. Cover and chill for 1 to 2 hours.
For the fudge sauce:
Combine 1/2 cup chocolate chips, cream, corn syrup, brown sugar, cocoa and salt in a heavy saucepan and bring to a boil, stirring frequently, over medium heat. Reduce heat to low and continue cooking at a gentle boil, stirring occasionally, for 5 minutes. Remove from the heat. Add the remaining 1/2 cup chocolate chips, butter and vanilla and whisk until glossy and smooth. Set aside.
For the whipped cream:
Just before serving, in the bowl of a stand mixer fitted with the whisk attachment (or with an electric mixer) beat the cream, confectioners' sugar and coffee liqueur until soft peaks just begin to form.
This can be assembled in a large trifle dish or individual glass serving dishes. Line up the individual dessert components. Break the devil's food cake into small pieces (it's okay if it crumbles; it will press into a cohesive layer in the trifle dish). Rewarm fudge sauce on low heat to thin, if necessary.
Spread a layer of chocolate mousse in the bottom of the dish. Arrange a fairly thick layer of devil's food cake pieces over the mousse. Drizzle fudge sauce over the cake pieces. Repeat layering, ending with mousse. Refrigerate trifle for 2 to 3 hours to set.
This dessert is best served at room temperature, so remove from the refrigerator at least an hour or two before serving. Top with fresh whipped cream and chopped chocolate-covered espresso beans. (If making individual trifles, top each trifle with one whole chocolate-covered espresso bean.)
NotesCook's Note: This cake can be made up to three days in advance; store in an airtight container at room temperature. Or to freeze, wrap tightly in plastic wrap, then aluminum foil, for up to 1 month. Defrost at room temperature before unwrapping.