via Clotilde's Chocolate and Zucchini blog
2 cups all-purpose flour
1/2 cup unsweetened cocoa powder
1 teaspoon baking soda
1/2 teaspoon baking powder
1/2 teaspoon fine sea salt
1 scant cup light brown sugar
1/2 cup) unsalted butter, at room temperature
1 teaspoon pure vanilla extract
1 teaspoon instant coffee granules or 2 tablespoons strong cooled coffee -- this is just to deepen the chocolate flavor, you won't taste it in the finished product
3 large eggs
2 cups unpeeled grated zucchini, from about 1 1/2 medium zucchini
1 cup good-quality bittersweet chocolate chips, or chopped chocolate
Confectioner's sugar to garnish
Preheat the oven to 350°F. Grease a 10-inch round springform pan.
In a medium mixing bowl, whisk together the flour, cocoa powder, baking soda, baking powder, and salt. In the bowl of a mixer (or by hand in a large mixing bowl), beat the sugar and butter until fluffy. Add the vanilla, coffee, and eggs, mixing well between each addition.
In a large mixing bowl, combine the zucchini, chocolate chips, and about a third of the flour mixture, making sure the zucchini strands are well coated and not clumping too much.
Add the rest of the flour mixture into the egg batter. Mix until just combined; the batter will be thick.
Fold the zucchini mixture into the batter, and blend with a spatula without overmixing. Pour into the prepared cake pan, and level the surface.
Bake for 40 to 50 minutes, until a knife inserted in the center comes out clean. Transfer onto a rack to cool for 10 minutes, run a knife around the pan to loosen, and unclasp the sides of the pan. Serve slightly warm or at room temperature. Sprinkle with confectioner's sugar or a chocolate glaze if desired.