Hot Fudge Cake

1 cup all-purpose flour
3/4 cup sugar
6 tablespoons baking cocoa, divided
2 teaspoons baking powder
1/4 teaspoon salt
1/2 cup milk
2 tablespoon vegetable oil
1 teaspoon vanilla extract
1 cup packed brown sugar
1-3/4 cups hot water
Whipped cream or ice cream, optional

In a medium bowl, combine flour, sugar, 2 tablespoons cocoa, baking powder and salt. Stir in milk, oil and vanilla until smooth. Spread in an ungreased 9-in. square baking pan. Combine brown sugar and remaining cocoa; sprinkle over batter. Pour hot water over all; do not stir. Bake at 350° for 35-40 minutes. Serve warm. Top with whipped cream or ice cream if desired.