MIX butter, brown sugar and vanilla thoroughly using an electric mixer. Beat in melted chocolate. Gradually blend in flour and corn starch.
PRESS dough into 13- x 9-inch ungreased baking pan.
BAKE in a preheated 300°F oven for 20 minutes. While bars are baking, unwrap caramels; place in a small saucepan with the cream. Heat until creamy, stirring constantly. Remove bars from oven and spread caramel topping over all. Sprinkle with chopped pecans. Return to oven for an additional 15 to 20 minutes. Cool.