Preheat oven to 425°F (218°C). Spray a 12-count muffin pan with nonstick spray or line with cupcake liners. This recipe yields about 10 muffins.

Whisk the flour, baking powder, baking soda, salt, cinnamon and nutmeg together in a large bowl. Set aside. In a medium bowl, whisk the oil, brown sugar, granulated sugar, egg, and vanilla extract together. Whisk in the zucchini. Pour the wet ingredients into the dry ingredients and whisk or stir until just combined. Avoid over-mixing.

Using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the cream cheese in a medium bowl on medium-high speed until smooth and creamy. Beat in the egg yolk, vanilla extract, and sugar until combined.

Spoon 1 heaping Tablespoon of zucchini muffin batter into the muffin cups. Layer with 1 Tablespoon of cream cheese filling, then another heaping Tablespoon of muffin batter—or however much batter is needed to fill the cups all the way to the top. Some cream cheese filling can poke out of the top or on the sides. Sprinkle with coarse sugar, if desired.

Bake for 5 minutes 425°F (218°C) then, keeping the muffins in the oven, reduce heat to 350°F (177°C)* and continue baking for another 15–17 minutes. The total time these muffins should be in the oven is around 20-22 minutes. Allow to cool for at least 10 minutes in the pan before serving.

Cover leftover muffins tightly and store at room temperature for up to 2 days, or in the refrigerator for up to 1 week.