Heat oven to 350°F Grease a 9 x 13 pan with cooking spray. Set aside.
Place butter in medium saucepan on the stove. Heat over medium heat until butter is melted. Remove from heat and stir in sugar and vanilla extract. Add eggs, one at a time, beating well with spoon after each addition. Add cocoa; stir until well blended. Add flour, baking powder and salt; stir until combined. Stir in Twix candy bar chunks. Pour batter into prepared pan.
Drizzle caramel evenly over the brownies. Using a toothpick, swirl caramel into brownies. Bake for 35-40 minutes or until brownies begin to pull away from sides of pan and a toothpick inserted in the middle comes out clean. Cool brownies completely in pan on a wire rack. Once cool, cut into squares and serve.