In a small saucepan over low heat, melt semisweet chocolate; cool 10 minutes.
In a small bowl, dissolve instant coffee in water. Add sour cream, sugar and vanilla; stir until sugar is dissolved. Blend in melted chocolate. Spread in prepared crust; set aside.
In a small mixer bowl, beat powdered sugar, cocoa and heavy cream until stiff peaks form. Mound mixture on top of chocolate layer. Garnish with chocolate sprinkles, if desired.