For the Ice Cream Cake:
Pulse cookies in food processor until fine crumbs form. Add melted butter and pulse to combine. Press into bottom of 9-inch spring form pan. Set aside.
Add 4 toffee bars to plastic bag. Use rolling pin to crush. Cut the 2 toffee bars into slices with serrated knife. Set aside for decoration.
Add sweetened condensed milk, espresso powder and coffee liqueur to bowl of electric mixer fitted with whisk attachment. Mix to combine. Add heavy cream and whip until soft peaks form. Fold in toffee pieces with rubber spatula.
Pour ice cream mixture over prepared crust. Spread evenly. Cover with plastic wrap and freeze for 6 hours or overnight.
For the Quick Caramel Sauce:
Add brown sugar, butter and cream to medium saucepan. Cook over medium-low heat, stirring constantly for 5 to 7 minutes or until thickened. Remove from heat and add vanilla, coffee liqueur, and salt. Allow to cool slightly.
Remove ice cream cake from freezer about 5 minutes before serving, just enough to allow it to soften but not melt. Top with whipped cream and decorate with remaining toffee bar pieces. Slice, and pour cooled caramel sauce over individual pieces.