Prepare Vanilla Semifreddo through step 2.

Drizzle one-third of melted chocolate all over whipped cream mixture. Freeze until chocolate is set, 4 to 5 minutes. Using a silicone spatula, break up chocolate and fold into whipped cream mixture. Repeat drizzling, freezing, and folding with remaining melted chocolate in two additions. Refrigerate.

Proceed with Vanilla Semifreddo recipe from step 3. Garnish with Chocolate Curls, if desired.