This is a towering brick of a 2.5-pound zucchini bread, easily 1.5x of most standard recipes, so please don’t balk at the oil or sugar levels — they’re all to scale, and the result is just moderately sweet. If you have a scale, this is a one-bowl recipe. You can use any kind of cocoa powder here, but my preference is Dutch-processed, or basically the kind you’d get from any European brand. Just a heads up: The baking time is long. It’s taken me 1 hour 25 minutes the last three tests, but I know that ovens range. You can cut into it right away but I really like it better on day two, when the moisture settles into an even crumb and the top is extra crunchy.
Place grated zucchini in a large bowl and add oil, eggs, sugars, vanilla, and salt. Whisk until combined. Sprinkle cinnamon, if using, baking soda, and baking powder over the surface of the batter and mix until combined — and then, for extra security that the ingredients are well-dispersed, give it 10 extra stirs. If your cocoa is lumpy, and mine always is, sift it over the batter. Add flour and mix until combined. Set 2 tablespoons chocolate chips aside and add the remaining to the batter, stirring to combine. Pour into the prepared loaf pan and smooth the top. Sprinkle with reserved chocolate chips and the raw or turbinado sugar — don’t skimp.
Bake for 1 hour 20 to 30 minutes. A toothpick inserted into the center of the cake won’t come out clean, because this bread is so fudgy, but it shouldn’t look like raw batter.
If you can bear it, letting it cool completely in the pan helps it set up. I leave mine in the pan overnight, unwrapped. To serve, carefully remove from the pan and serve in slices.
Do ahead: This zucchini bread keeps for up to one week in the fridge, yes, fridge — although it won’t go bad at room temperature (for 2 to 3 days). It’s so fudgy, I think it’s best kept cold. I store the double chocolate zucchini bread in the cake pan with the top uncovered, to keep it crunchy. I press a piece of plastic or foil only against the cut end of the cake.
