Set oven to 350 degrees F. Lightly spray a 9" x 13" x 2" baking pan with vegetable spray. Prepare brownie mix according to package directions; stir in pecans. Spread batter in prepared pan and bake 25-30 minutes until toothpick inserted in center comes out clean. Sprinkle immediately with marshmallows. Cool on a wire rack. In large saucepan, combine marshmallow creme, milk, butter, cocoa and chocolate. Cook and stir over low heat until melted and smooth. Beat in powdered sugar and vanilla until smooth. Drizzle over marshmallows. Yield: 24 brownies.