01 -
Preheat oven to 350° F. Grease a 9 x 5 inch loaf pan with non-stick baking spray and line with parchment paper. Allow the short sides of parchment to hang over the edge of the pan to facilitate easy removal.
02 -
Using a box grater, shred a medium to large zucchini. Measure about 1 3/4 cups loosely packed shredded zucchini. Wrap in two layers of paper towels or a dishcloth and pat to remove excess moisture. Set aside.
03 -
In a large bowl, whisk the melted butter and sugar together until well combined and pale in color. Add the egg and egg yolk, mixing until fully incorporated. Add the vanilla and sour cream, whisking until smooth. Stir in the shredded zucchini.
04 -
In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
05 -
Add the dry ingredients to the zucchini mixture in two additions. Using a spatula or wooden spoon, gently fold the flour mixture into the wet ingredients. Avoid over-mixing. Gently stir in the chocolate chips.
06 -
Transfer the batter to the prepared loaf pan and smooth the top. Sprinkle reserved chocolate chips evenly over the batter.
07 -
Bake for 45 to 50 minutes, checking halfway through. If the top is browning too quickly, loosely cover it with a piece of aluminum foil. Bake until the edges are set and a toothpick inserted into the center comes out clean or with a few crumbs attached.
08 -
Remove the loaf from the oven and cool in the pan for 20 to 30 minutes. Use the parchment paper overhang to carefully lift the loaf from the pan. Transfer to a wire rack to cool completely for clean slices or serve warm.