Preheat the oven to 350°F (180°C) and line two 6-cup muffin pans with 9 cupcake liners.
In a large bowl, whisk together flour, baking powder, baking soda, pumpkin pie spice, cinnamon, and salt.
1 cup all-purpose flour, ¾ teaspoon baking powder, ½ teaspoon baking soda, 1 teaspoon pumpkin pie spice, ½ teaspoon ground cinnamon, ¼ teaspoon salt
In another bowl, whisk the brown sugar and oil until smooth. Add the egg, pumpkin purée, and vanilla extract, whisking until fully combined.
½ cup light brown sugar, 1 large egg, 1 cup pumpkin purée, ¾ teaspoon vanilla extract, ¼ cup vegetable oil
Pour the wet ingredients into the dry ingredients and gently fold with a spatula until just combined. Do not overmix.
Fill each cupcake liner halfway to two-thirds full.
Bake for 18–20 minutes, or until a toothpick inserted in the center comes out mostly clean.
Let the cupcakes cool completely on a wire rack before frosting.