Preheat the oven to 375 degrees F.: When you open the oven later, you want a steady, even heat so the muffins rise and set properly, and that initial warmth encourages an even crust. As the oven warms, you might notice a faint, dry heat and the faint scent of warm metal; that tells you the chamber is ready. Give the oven at least 10 to 15 minutes to fully stabilize if it has been cold, because an underheated oven can cause flat, dense tops. Avoid the mistake of putting muffin pans in immediately after turning the oven on, since that traps steam and prevents the quick initial lift needed for a tender, lofty muffin.
Line a muffin tin with paper liners and spray them with nonstick cooking spray. Set aside.: Lining the tin ensures easy removal and a clean presentation, and the spray helps prevent sticking while keeping the exterior edges slightly crisp. Press the liners into each well so they sit flush, and you may hear a faint tearing sound as you smooth them in. If you skip liners, grease the wells well to avoid tearing when unmolding, which is a common pitfall. I like using liners for quick cleanup and a uniform look.
In a medium bowl, whisk together the flour, cinnamon, baking powder, baking soda, salt, ginger, nutmeg, and cloves. Set aside.: Whisking the dry ingredients distributes the spices and leaveners evenly, so each muffin has consistent flavor and rise. You should see a uniform, pale tan mixture with darker specks of spice throughout, and the aroma will already hint at warm, inviting notes. A common mistake is to dump spices without mixing, which creates hot spots of flavor or uneven lift. I take a moment to sift any clumps so the batter mixes smoothly later.
In a large bowl, whisk together the pumpkin, maple syrup, oil, eggs, and vanilla extract.: The wet mixture should look glossy and cohesive, with the deep orange of the pumpkin puree bright against the liquid ingredients. Whisking by hand or with a mixer until smooth ensures the eggs are fully incorporated, which helps trap air for a lighter crumb. You will smell the maple and vanilla blending with the pumpkin, a comforting aroma that foreshadows the finished muffin. Avoid overbeating, which can incorporate too much air and collapse during baking, causing tunnels or an uneven crumb.
Add the dry ingredients to the wet ingredients and stir until just combined, don’t over mix. Gently fold in the zucchini and chocolate chips, if using.: After combining, the batter should be slightly thick and speckled with spice, not glossy like a cake batter. Folding in the shredded zucchini introduces delicate green flecks and added moisture, and the chocolate chips provide little pockets of molten richness when warm. You should stop mixing when streaks of flour disappear, because over mixing activates gluten and leads to a tough muffin. A common error is vigorous mixing, which creates a chewy texture, so be gentle with a spatula and use a folding motion.
Divide the batter equally amongst the muffin cups. Sprinkle each muffin with turbinado sugar.: Spoon or use a scoop to portion the batter evenly, filling cups about two thirds full for a domed top. You will see the batter settle and the surface level out, and when sprinkled with turbinado sugar the tops gain a sparkling, bristly sheen that caramelizes slightly in the oven. Uneven portions will bake at different rates, so take a moment to level the cups for uniform browning. Avoid overfilling, which causes spillover and uneven baking.
Bake for 18 to 23 minutes or until the muffins are golden brown and the tops of the muffins bounce back when you gently press on them. You can also insert a toothpick into the center of a muffin, if it comes out clean, they are done.: During baking the kitchen will fill with spice and a roasted pumpkin scent, and you may hear faint crackling as the tops set. The visual cues are key, look for a warm golden color and slight doming. Press the top lightly; a springy response indicates the interior is set, while a soft indentation suggests more time is needed. A toothpick inserted into the center can confirm doneness if it comes out clean or with just a few moist crumbs. Be careful not to overbake, which dries the crumb and dulls the spices.
Let the muffins cool in the pan for 5 minutes. Remove muffins from the tin let cool another 15 minutes.: Cooling briefly in the pan lets the structure stabilize so the muffins do not fall apart when removed, and transferring them to a rack finishes the cooling while allowing steam to escape so the bottoms do not become soggy. You will notice a warm, fragrant steam rising as they cool, and the texture firms to the ideal tender crumb. A common mistake is to let them sit too long in the hot pan, which can overcook the bottoms and create a denser texture. After cooling, they should be pleasantly warm and ready to enjoy or store for later.