Preheat oven to 350 degrees. Add cupcake liners to a 12-cupcake pan, or grease pan.
Mix flour (or flour+baking powder), salt, and pumpkin spice in medium bowl. Set aside.
Combine pumpkin puree, milk, and vanilla extract in a medium bowl. Set aside.
Cream brown sugar, sugar, and butter in the bowl of your stand mixer. Add eggs in thirds, mixing thoroughly between additions.
With your stand mixer on low, beat in flour mixture in thirds, alternating with half of the pumpkin puree, until all is combined.
Using an ice cream scoop, fill each section in the cupcake pan 3/4 full. Bake for 20-25 minutes, or until a toothpick inserted comes out clean. Repeat for second dozen.