Step 1: Preheat and Prep Preheat your oven to 425°F (218°C). Line a 12-count muffin tin with paper liners or grease them well with non-stick spray. Starting with a very hot oven is the secret to getting those tall, domed bakery tops.
Step 2: Mix Dry Ingredients In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, brown sugar, baking soda, salt, pumpkin pie spice, and cinnamon. Ensure there are no large lumps of brown sugar remaining.
Step 3: Combine Wet Ingredients In a separate medium bowl, whisk the eggs until lightly beaten. Add the pumpkin puree, oil, milk, and vanilla extract. Whisk until the mixture is completely smooth and well combined.
Step 4: Fold the Batter Pour the wet ingredients into the dry ingredients. Using a spatula, gently fold the mixture together until just combined. Be careful not to overmix, as this can make the muffins tough; it is okay if a few small streaks of flour remain.
Step 5: Fill the Muffin Tin Divide the batter evenly among the 12 muffin cups. They should be filled almost to the very top. If desired, sprinkle the tops generously with coarse sparkling sugar for a crunchy texture.
Step 6: Bake and Adjust Temperature Place the muffins in the oven and bake at 425°F for exactly 5 minutes. Without opening the oven door, reduce the temperature to 350°F (177°C). Continue baking for another 15 to 18 minutes, or until a toothpick inserted into the center comes out clean.
Step 7: Cool Allow the muffins to cool in the pan for 5 to 10 minutes. Transfer them to a wire rack to cool completely. This prevents the bottoms from becoming soggy due to steam.