replace milk/water in the recipe with freshly brewed espresso. Add a shot (or two) of kahlua (coffee liqueur)
Chocolate Swiss Meringue Buttercream
2 large egg whites
2 sticks unsalted butter, softened
1 t vanilla
90g dark chocolate, 70% cocoa
Whisk the egg whites with sugar over a bain marie until warm. Transfer mixture into the mixer and whip until it turns white and about doubles in volume. Add the vanilla. Finally, add the butter a stick at a time and whip. When amalgamated and smooth, whisk in the melted dark chocolate.