Put the buttermilk, vegetable oil, granulated sugar, brown sugar, eggs, and vanilla in a bowl. Whisk until combined.
In a separate bowl, combine the flour, baking powder, ground cinnamon, baking soda, salt, and ground nutmeg. Add to the wet ingredients and stir until combined. Set aside for 15-20 minutes.
While waiting, preheat the oven to 425˚F and line a 12-count muffin pan with cupcake liners. Then, prepare the crumb topping by combining the flour, brown sugar, and ground cinnamon. Stir in the melted butter until crumbly and set aside.
Stir the shredded zucchini into the batter.
Fill the lined muffin cups with batter. Top with the crumble topping and gently press on it to help it stick.
Bake at 425˚F for 5 minutes. Then, leaving the pan in the oven, turn it down to 350˚F and continue baking the muffins for 16-18 minutes or until a toothpick inserted in the center comes out clean.
Cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
Beat the softened cream cheese until smooth. Add the powdered sugar, whole milk, and vanilla extract. Beat until smooth. Drizzle with cream cheese glaze over the muffins.
Video
Notes
Line an airtight container with paper towels before adding the cooled muffins. Store them at room temperature for 1-2 days, in the fridge for 3-4 days, or in the freezer for 2-3 months.