Heat oven to 350°F. Line 13 x 9 x 2-inch baking pan with nonstick foil or with regular foil coated with nonstick spray.
In large microwave-safe bowl, melt together butter and chocolate in microwave oven on high for 2 minutes; stir until smooth. Whisk in eggs, sugar, flour 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 in 350°F oven until top is dry to the touch, about 35 minutes. Let cool completely in pan on wire rack. Lift brownie from pan with foil. Cut into squares.