A perennial favorite at Moosewood.
1. Preheat oven to 375°F. Generously oil 8-inch square or round baking pan. Dust with sifted cocoa, or line bottom of baking pan with parchment paper.
To make Chocolate Cake:
2. Sift flour, cocoa, soda, salt and sugar. In another bowl, combine oil, water or coffee and vanilla. Pour liquid into dry, and mix until smooth.
3. Add vinegar and stir briefly; baking soda will begin to react with vinegar, leaving pale swirls in batter. Without wasting time, pour batter into prepared pan.
4. Bake for 25 to 30 minutes. Serve cake from pan, or, when cool, transfer to plate.
To make Chocolate-Peanut Butter Frosting:
5. In heavy saucepan, melt chocolate over medium heat. Beat together peanut butter, water and vanilla until smooth. Beat in confectioners’ sugar, and add melted chocolate, mixing until blended. Spread frosting on cooled cake.