Bake brownies according to package directions in a 9x13 pan. Let cool completely, then flip out onto a cutting board. Using a 3-inch round cookie cutter, cut out 12 circles from the brownie sheet.
Line a 12-cup muffin tin with plastic wrap, letting the wrap hang over the edges. Press one brownie circle into each cup, molding it to create a bowl shape that covers the bottom and sides.
Scoop about 2 tablespoons of softened ice cream into each brownie-lined cup. Press down gently to eliminate air pockets. Add 1 teaspoon of Nutella to the center of each, then top with another tablespoon of ice cream.
Place another brownie circle on top, pressing the edges to seal everything together. Wrap the plastic overhang tightly around each bombe and freeze for at least 3 hours or overnight.
Once completely frozen, unwrap and dip each bombe into the melted chocolate mixture, then roll in Heath toffee bits. Return to the freezer for 30 minutes to set the chocolate coating.
Let sit at room temperature for 5 minutes before serving. Serve with extra caramel sauce or whipped cream if desired.
