Line side of 7-inch (1.5 L) springform with parchment paper; set aside. Stir cookie crumbs with butter; pat onto bottom of pan. Bake in centre of oven for about 7 minutes or until firm. Let cool on rack.
In heatproof bowl over saucepan of hot (not boiling water), melt semisweet chocolate, stirring occasionally; let cool to room temperature.
In separate bowl, whisk together coffee granules, boiling water and cocoa; set aside.
In large heatproof bowl over saucepan of simmering water, beat eggs with sugar for 5 minutes or until thickened. Reduce speed to low; beat in coffee mixture and melted chocolate. Let cool to room temperature, about 20 minutes.
In another bowl, whip cream; fold one-quarter into chocolate mixture. Gently fold in remaining whipped cream. Pour over crust, smoothing top.
Pipe or drizzle white chocolate decoratively over top. Garnish with semisweet chocolate. Freeze for at least 6 hours or until firm. (Make-ahead: Semifreddo can be wrapped in plastic wrap and stored in rigid airtight container for up to 1 week.)
Partially thaw in refrigerator for 1 hour before unmoulding to serve.