1 2/3 c. all-purpose flour
1 c. packed brown sugar
1/2 c. cocoa
1 tsp. baking soda
1/2 tsp. salt
1 c. (2 sticks) butter
1 c. warm water
1/3 c. vegetable oil
1 tsp. vinegar
1/2 tsp. vanilla
1/2 c. chocolate chips

Heat oven to 350°F. Mix flour, sugar, cocoa, baking soda and salt with fork in ungreased 8x8x2-inch pan. Mix in remaining ingredients except chocolate chips. Sprinkle chocolate chips over batter. Bake until wooden pick inserted in center comes out clean, about 35 to 40 minutes. Sprinkle with powdered sugar, if desired.