Piped in an elegant swirl, this mocha mousse is a gorgeous and delicious filling for store-bought chocolate shells.
Make the sugar syrup: Bring sugar and 1/2 cup water to a boil in a small saucepan. Swirl pan to dissolve sugar. Remove from heat, and let cool until just warm.
Melt chocolate in a heatproof bowl set over a pan of simmering water. Stir until smooth; set aside. Whisk cream in a large bowl until stiff peaks form; set aside.
Put 2 tablespoons cold water in a small heatproof bowl; sprinkle with gelatin. Let soften about 5 minutes. Set bowl over a pan of simmering water; stir until gelatin has completely dissolved. Remove from heat, and stir in 3 tablespoons warm sugar syrup and the espresso powder. Whisk mixture into melted chocolate.
Whisk 1/3 of whipped cream into chocolate mixture. Fold in remaining whipped cream until combined. Put mousse in a pastry bag fitted with a large star tip (such as Ateco #826). Fill each tulip shell with mousse. Serve with chocolate sauce.