2/3 cup self-rising flour
3 tablespoons cocoa
1/4 teaspoon baking soda
1/3 cup granulated sugar
1 tablespoon butter
1/3 cup water
1 egg

Peppermint Filling
2 1/4 cups confectioners' sugar
1 tablespoon oil
2 tablespoons milk
1/2 teaspoon peppermint extract

Chocolate Topping
4 (4 ounce) squares dark chocolate, chopped
3 tablespoons unsalted butter

Grease a 15 x 10-inch jellyroll pan; line with greased paper.

Sift flour, cocoa and baking soda into small bowl of electric mixer; add sugar, butter and water. Beat on medium speed for two minutes. Add egg; beat until combined. Spread mixture into prepared pan. Bake at 350 degrees F for about 20 minutes; cool in pan.

Peppermint Filling: Combine confectioners' sugar and oil in a small heatproof bowl; stir in enough milk to make a stiff paste. Add peppermint extract. Stir over hot water until spreadable.

Chocolate Topping: Melt chocolate and butter over hot water.

Spread cooled base with Peppermint Filling; refrigerate until set. Spread with Chocolate Topping; refrigerate until set before cutting.