Line a 9-inch springform pan with parchment paper. Crush chocolate sandwich cookies into fine crumbs using a food processor. Mix with 6 tablespoons melted butter until combined. Press firmly into the bottom of the prepared pan. Freeze for 15 minutes.

Spread vanilla ice cream evenly over the frozen crust using an offset spatula. Smooth the top and return to freezer for 30 minutes.

Make the caramel: Combine sugar and water in a heavy-bottomed saucepan over medium heat. Stir gently until sugar dissolves. Stop stirring and cook until mixture turns deep amber color, about 8-10 minutes.

Carefully pour in warm heavy cream while stirring constantly. Add 4 tablespoons butter and sea salt. Stir until smooth. Cool to room temperature.

Drizzle cooled caramel over the frozen ice cream layer. Return to freezer for 30 minutes.

Make the ganache: Heat 3/4 cup heavy cream until just simmering. Pour over chopped dark chocolate in a bowl. Let sit 2 minutes, then stir until smooth and glossy.

Pour ganache over the caramel-topped cake, encouraging drips down the sides. Freeze for at least 6 hours or overnight before serving.

To serve, run a hot knife around the edge and release the springform pan. Let sit at room temperature for 5 minutes before slicing. Garnish with additional caramel or chocolate shavings if desired.