Preheat oven to 350°. Butter four 2-by-6-inch miniature-loaf pans (2 inches deep; not nonstick). In a medium bowl, whisk together cocoa powder and 6 tablespoons hot water. Stir half the batter into cocoa mixture.

Spoon 2 dollops of batter into pan next to each other, 1 chocolate and 1 vanilla. Repeat twice, alternating layers.

Insert a knife or skewer vertically all the way down to the bottom of the pan, then swirl together the alternating vanilla and chocolate layers to create a marbled effect.

Bake until a skewer inserted in center of a cake comes out with a few moist crumbs attached, 40 to 45 minutes, rotating pans halfway through. Let cool completely in pans on a wire rack. Run a knife around edges, then turn out cakes. (Store in an airtight container at room temperature, up to 3 days)

per serving: 292 cals: 14g fat (9g sat fat): 5g protein: 39g carbs: 1g fiber