Start by combining the heavy cream and butter in a saucepan. Heat gently over medium heat. Stir continuously until the butter melts and the mixture is hot but not boiling.

Add the light corn syrup and light brown sugar to the hot cream mixture. Stir until fully dissolved. This creates a rich, sweet base for your sauce.

Remove from heat and add the chopped bittersweet chocolate. Whisk until smooth. Add cocoa powder and stir in the dark rum and vanilla extract.

Let the fudge sauce cool to room temperature. It should thicken as it cools. You can store it in an airtight container for up to two weeks in the refrigerator.

While the sauce cools, take your chilled vanilla custard or store-bought soft serve. You can also use a homemade base if you're feeling ambitious.

Fold in espresso powder, dark chocolate, cookie dough chunks, and chocolate truffles into the custard base. Pearls of chocolate and rich cookie dough will mix beautifully with the creamy texture.

Spoon the mixture into cups or bowls. Drizzle generous helpings of chilled fudge sauce over the top and finish it with chocolate sprinkles.