Brownie Carrot Cake

1 (19.8 ounce) box fudge brownie mix
4 large eggs
2 cups grated carrots
1 1/2 cup mayonnaise
1 cup granulated sugar
1 teaspoon ground cinnamon
1 teaspoon vanilla extract
1 cup chopped pecans
Confectioners' sugar (optional)

Combine first 7 ingredients in a large mixing bowl; beat at low speed with electric mixer 2 minutes. Stir in chopped pecans. Pour into greased 13 x 9-inch pan; bake at 350 degrees F for 50 to 55 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on wire rack. Cut into squares. Dust with confectioners' sugar, if desired.