How to Make It
Preheat oven to 350°.
To prepare brownies, weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 4 ingredients (through baking powder) in a large bowl, stirring well with a whisk. Combine 6 tablespoons butter, eggs, and 1 teaspoon vanilla. Add butter mixture to flour mixture; stir to combine. Scrape batter into a 9-inch square metal baking pan lightly coated with cooking spray. Bake at 350° for 19 minutes or until a wooden pick inserted in center comes out with moist crumbs clinging. Cool in pan on a wire rack.
To prepare topping, melt 1/4 cup butter in a saucepan over medium heat. Add 1/4 cup brown sugar and 1 1/2 tablespoons milk; cook 2 minutes. Remove from heat. Add vanilla and powdered sugar; stir with a whisk until smooth. Spread mixture evenly over cooled brownies. Let stand 20 minutes or until set.
Combine 2 tablespoons milk and chocolate in a microwave-safe bowl; microwave at HIGH for 45 seconds or until melted, stirring after 20 seconds. Stir just until smooth; drizzle over caramel. Sprinkle with sea salt; let stand until set. Cut into squares.