Preheat the oven. Preheat the oven to 350 degrees F. Grease a 9x13-inch metal baking pan. Set aside.
Bake the brownies. In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth. Whisk in the eggs and vanilla extract until combined. Add the flour, cocoa powder, espresso powder, if using, and salt. Stir until just combined. Fold in 3/4 cup of the chopped chocolate. Spread the batter evenly into the prepared pan. Sprinkle the remaining 1/4 cup chopped chocolate over the top. Bake for 24 to 28 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Do not overbake. Let the brownies cool completely in the pan.
Make the Ice Cream Layer. In a large bowl, gently fold the Heath Toffee Bits into the softened vanilla ice cream. Spread the ice cream evenly over the chilled brownies.
Add the Caramel. Drizzle the salted caramel sauce evenly over the ice cream. If needed, microwave the caramel for a few seconds until it's smooth and easy to drizzle, but don't let it get warm. Freeze the cake for 30 minutes, or until the ice cream layer is set a little firm.
Make the Whipped Cream. In the bowl of a stand mixer fitted with the whisk attachment (or using a hand mixer), beat the heavy cream, confectioners' sugar, and vanilla until medium-stiff peaks form.
Assemble the Cake. Spread the whipped cream evenly over the caramel layer. Sprinkle with the Heath Toffee Bits.
Freeze. Freeze the cake for at least 4 hours or overnight before serving.
Serve. Let the cake sit at room temperature for 5 to 10 minutes before slicing. For clean slices, dip a sharp knife in hot water and wipe it dry between cuts. Serve with a drizzle of salted caramel sauce on top, if desired.
Notes
Make sure the brownies are completely cool before adding the ice cream layer.
Soften the ice cream just enough to make it easy to fold in the toffee bits and spread over the brownies. Do not let it melt.
If the caramel sauce is too thick to drizzle, warm it briefly, then let it cool before adding it to the ice cream.
Freeze the cake for at least 4 hours, but overnight is ideal for the cleanest slices.
Let the cake sit at room temperature for 5 to 10 minutes before slicing.
For clean slices, run a sharp knife under hot water and wipe it dry between cuts.
Serve with an extra drizzle of salted caramel sauce, if desired.
The cake can be made in advance and kept tightly covered in the freezer.