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  1. Combine the starter, milk, and flour in a large mixing bowl. Cover and let rest at room temperature for 2 to 3 hours. It won't necessarily bubble, but it may have expanded a bit.

  2. Preheat the oven to 350°F. Lightly grease a 9" x 13" pan.

  3. In a separate bowl, beat together the sugar, oil, vanilla, salt, baking soda, cocoa. and espresso powder. The mixture will be grainy.

  4. Add the eggs one at a time, beating well after each addition.

  5. Gently combine the chocolate mixture with the starter-flour-milk mixture, stirring till smooth. This will be a gloppy process at first, but the batter will smooth out as you continue to beat gently.

  6. Pour the batter into the prepared pan.

  7. Bake the cake for 30 to 40 minutes, until it springs back when lightly pressed in the center, and a cake tester inserted into the center comes out clean.

  8. Remove the cake from the oven, and set it on a rack to cool while you make the icing. You're going to ice the cake right in the pan, so don't worry about turning it out.

  9. Sift the confectioners' sugar into a large mixing bowl, and set it aside.

  10. In a small saucepan set over medium heat, melt the butter and add the buttermilk or yogurt. Dissolve the espresso powder in the hot water, add to the pan, and bring the mixture just to a boil.

  11. Immediately pour the simmering liquid over the confectioners' sugar in the bowl, and beat until smooth.

  12. Pour the warm frosting over the cake. Yes. it's thin and pourable; don't worry, it'll set as it cools. If you wait too long and the frosting stiffens up, simply spread it over the cake rather than pouring it.  

  13. Combine the chocolate chips, milk, and corn syrup in a microwave-safe cup. Microwave until the chips soften, then stir until smooth.

  14. Drizzle/drip the chocolate over the icing. You can do this while the icing is still warm, or wait until it's cooled.

Tips from our Bakers

  • Don’t have any starter? Here’s a recipe for homemade sourdough starter. If you're making it from scratch, you'll need to feed it for 5 to 7 days before it’s ready for baking. Want a head start? Purchase our classic fresh sourdough starter — it’ll be ready for baking soon after it arrives at your door. Looking for tips, techniques, and all kinds of great information about sourdough baking? Find what you need in our sourdough baking guide.

  • Do you really need the espresso powder in the cake? Well, certainly it's not critical to the cake's structure. But we find espresso powder heightens chocolate flavor, just as vanilla does. You can't really taste either one; but each is a lovely accent to chocolate, bringing out the nuances of its flavor.
  • How do you tell when a cake is done? Start with the time it's been in the oven, certainly, but don't depend on that; ovens vary wildly in how they bake. Rely instead on the usual tests: is the cake barely beginning to pull away form the sides of the pan? Does it spring back when pressed lightly in the center (rather than your finger leaving an imprint)? And, most importantly, does a cake tester or toothpick inserted into the center come out clean, or with perhaps only a few solid crumb clinging to it? Then, no matter what your timer says, the cake is done.