Preheat the oven to 375°F: Line a standard muffin pan with muffin liners, or grease each well with butter.
Mix the dry ingredients: In a large mixing bowl, whisk together the flour, pumpkin pie spice, baking powder, baking soda, and salt.
Mix the wet ingredients: In a medium mixing bowl, add the pumpkin purée, brown sugar, eggs, and vegetable oil. Whisk until combined and homogenous.
Make the batter: Pour the pumpkin mixture into the flour mixture. Stir with a large spoon or a rubber spatula just until combined and no streaks of flour remain. Do not overmix. It is okay if there are some lumps in the batter.
Divide the muffin batter: Divide the batter evenly among the cups. Each well should be filled nearly to the top.
Bake the muffins: Bake muffins for 20 minutes, or until a toothpick inserted in the center of the muffin comes out clean.
Cool the muffins and serve: Allow the muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool for at least 10 minutes more. Serve warm or at room temperature.
