1. Preheat oven to 350F. Coat a 13 x 9-inch glass baking pan with cooking spray.
2. To prepare cake, sift together flour, cocoa, baking soda, baking powder and salt into a large bowl.
3. Combine oil and sugar in a large mixing bowl. Using a mixer, beat at medium speed until well combined. Add eggs; beat well. Add flour mixture alternately with milk, beginning and ending with flour mixture, beating well after each addition and scraping down the sides of the bowl. Stir in the coffee and vanilla (batter will be thin).
3. Pour batter into prepared pan. Bake 35 to 40 minutes, until a wooden toothpick inserted near the center comes out clean. Cool completely on a wire rack.
4. To prepare frosting, combine cream cheese and peanut butter in a large mixing bowl. Using a mixer, beat at medium speed until smooth. Add powdered sugar, milk and vanilla; beat until smooth. (If frosting is too thin, add more powdered sugar; if it is too thick, add more milk.) Spread frosting over top of cooled cake and sprinkle with chocolate chips, if using. Store in the refrigerator. Serves 16.