Melt butter in a 9x13 pan in oven. Mix flour, sugar, and cocoa. Add eggs, vanilla, melted margarine. Beat well by hand. Spread mix in pan. Fold in chocolate chips.
Bake 325º for 25-30 minutes. Frost with milk chocolate brownie frosting.
Milk Chocolate Brownie Frosting
3 Tablespoons margarine
2 Tablespoons cocoa
1 1/2 cup confectioners' sugar
2 tablespoons milk
1 teaspoons vanilla
Melt margarine in microwave. Stir in cocoa, milk, and vanilla. Add confectioners' sugar. Stir until smooth. Add more milk if needed to make soft spreading consistency. Frost cool brownies, let set until firm.