Preheat the oven: Preheat your oven to 350°F (175°C). Line 18 muffin cups with paper liners.
Mix dry ingredients: In a small bowl, whisk together the flour, baking powder, baking soda, salt, and pumpkin pie spice. Set aside.
Mix wet ingredients: In a stand mixer fitted with the paddle attachment, mix the pumpkin puree, vegetable oil, eggs, and 1 1/4 cups of sugar on low speed until well combined.
Combine wet and dry: Add the flour mixture to the wet ingredients and mix on low speed until just combined. Be careful not to overmix.
Prepare topping: In a small bowl, stir together the remaining 1 tablespoon of sugar and the cinnamon.
Fill and bake: Divide the batter evenly among the muffin cups, filling each about 2/3 full. Sprinkle the cinnamon-sugar topping evenly over each muffin.
Bake: Bake for 20–25 minutes, or until the muffins are puffed, golden brown, and a toothpick inserted into the center comes out clean.
Cool and serve: Let the muffins cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
Notes
Store in an airtight container at room temperature for up to 3 days or refrigerate for up to 1 week.
Wrap individually and freeze for up to 3 months. Thaw at room temperature or warm in the microwave for 15–20 seconds.
Optional add-ins: Mix in 1/2 cup chocolate chips, chopped nuts, or dried cranberries for extra flavor and texture.