Heat oven to 350°. Line 13 x 9 x 2-inch baking pan with nonstick foil.
In large microwave-safe bowl, melt together butter and chocolate in microwave oven for 2 minutes; stir until smooth. Whisk in eggs, sugar, fl our and vanilla. Stir in pecans. Spread half the batter into prepared pan. Sprinkle with 1 cup chocolate chunks.
In medium-size saucepan, melt together caramels and heavy cream over medium-low heat until smooth, about 5 minutes. Evenly pour over batter in pan. Spread with remaining batter. Sprinkle with remaining 1 cup chocolate chunks.
Bake at 350° for about 35 minutes or until top is dry to the touch. Let cool completely in pan on wire rack. Grab foil and lift brownie from pan. Cut into squares and serve.