1. Preheat oven to 350°. Bake pecans in a single layer in a shallow pan 6 to 8 minutes or until lightly toasted and fragrant.
2. Microwave chocolate and 3/4 cup butter in a large microwave-safe bowl at HIGH 1 to 1 1/2 minutes or until melted and smooth, stirring at 30-second intervals. Whisk in sugar and eggs until well blended. Stir in flour. Spread batter into a greased 13- x 9-inch pan.
3. Bake at 350° for 25 to 30 minutes or until a wooden pick inserted in center comes out with a few moist crumbs. Let cool 1 hour on a wire rack.
4. Combine brown sugar, milk, 2 Tbsp. butter, and salt in a large saucepan; bring to a boil over medium-high heat, stirring occasionally. Reduce heat to medium-low, and simmer, stirring occasionally, 5 minutes or until slightly thickened. Remove from heat. Let stand 5 minutes. Beat in powdered sugar and vanilla at medium speed with an electric mixer until smooth. Pour over brownies, spreading to edges; sprinkle with toasted pecans. Let cool 30 minutes. Cut into squares.