Preheat oven to 350°. Beat butter at medium speed with an electric mixer until fluffy; gradually add brown sugar, beating well. Add eggs, 1 at a time, beating just until blended after each addition. Stir in pecans, flour, vanilla, and salt. (Batter will be thick.) Lightly grease a 13- x 9-inch pan with cooking spray. Spread batter in prepared pan. Bake 25 to 30 minutes or until a wooden pick inserted in center comes out clean. Cool completely on a wire rack (about 1 hour). Cut into 16 squares.