Preheat oven to 350 degrees F.
Spray a 13 by 9-inch pan with vegetable oil spray.
In a glass or ceramic bowl, melt the butter in the microwave. Whisk in the sugar, eggs, cocoa, and vanilla. Stir in the flour and salt. Add chopped semisweet and bittersweet chocolates and pecans.
Spread the batter in prepared pan. Bake about 25 minutes, just until brownies test moist but not wet. Cool completely before cutting.