Preheat oven to 350°F. Grease one 8x4 loaf pan or three mini loaf pans.
For the crumb topping: In a small bowl, mix the flour, brown sugar, cinnamon, and cold butter with a fork or pastry cutter until crumbly. Set aside.
In another bowl, whisk together the flour, baking powder, baking soda, salt, nutmeg, and cinnamon.
In the bowl of a stand mixer, mix the eggs, white sugar, brown sugar, sour cream, oil, and vanilla extract until smooth.
Add the dry ingredients to the wet and mix until just combined.
Fold in the grated zucchini.
Pour the batter into the prepared pan(s) and sprinkle the crumb topping evenly over the top.
Bake large loaf for 60 minutes or mini loaves for 45 minutes, or until a toothpick inserted in the center comes out clean.
Let cool in the pan for 10 minutes, then transfer to a wire rack.