1FOR ICE CREAM: Place ice cream in medium bowl and soften slightly at room temperature.
2Stir in chopped toffee bars and over bowl with plastic wrap and freeze. (Can be prepared 3 days ahead)
3FOR CARAMEL SAUCE: Bring whipping cream to simmer in heavy small saucepan and set aside.
4Combine sugar and 3 tablespoons water in heavy medium saucepan.
5Stir over medlium heat until sugar dissolves and increase heat to high and boil without stirring until caramel is deep amber color.
6Brushing down sides of pan with wet pastry brush if sugar crystals form and occasionally swirling pan, about 8 minutes.
7Remove from heat and slowly add warm whipping cream (mixture will bubble vigorously).
8Return sauce to low heat and stir until smooth.
9Remove from heat and mix in butter. (Can be prepared 3 days ahead. Cover and refrigerate.)
10FOR BROWNIES: Preheat oven to 350 degrees.
11Butter 9" square baking pan with 2" high sides.
12Combine butter and both chocolates in top of double boiler set over simmering water; stir until melted.
13Remove from over water and cool mixture slightly.
14Using electric mixer, beat eggs, sugar and vanilla in large bowl until slightly thickened, about 1 minute.
15Beat in chocolate mixture.
16Add flour, baking powder and salt and mix until combined.
17Stir in all but 2 tablespoons chopped toffee bars and transfer batter to prepared pan.
18Sprinkle with remaining 2 tablespoons chopped candy.
19For fudgy consistency, bake until tester inserted into center comes out with moist batter still attached, about 27 minutes; for cakelike texture bake until tester inserted into center comes out with a few moist crumbs attached, about 35 minutes.
20Cool. (Can be prepared 1 day ahead. Cover and store at room temperature.)
21Rewarm sauce over low heat and cut brownie into 9 pieces.
22Spoon warm caramel sauce onto 8 plates.
23Place 1 brownie in center of each (reserve extra brownie for another use) and surround each with 3 small scoops of ice cream.