Preheat the oven to 350 and line a 12-count muffin pan with muffin liners.
Mix the flour, baking soda, baking powder, salt, pumpkin spice, and cinnamon in a medium bowl.
In a stand mixer, mix the eggs, oil, vanilla, pumpkin puree, and brown sugar until well combined.
Slowly add the dry ingredients to the wet ingredients, mixing with a rubber spatula until fully combined but not smooth.
Use a 2-inch cookie scoop to place a heaping scoop of batter into each muffin well.
Bake the muffins for 22 to 26 minutes until a toothpick inserted into the center comes out clean.
Cool the muffins for about 5 minutes in the pan. Then, transfer them to a wire rack to cool completely.
Cinnamon Cream Cheese Frosting
Beat the butter and cream cheese for 2 minutes in a stand mixer.
Add the remaining ingredients and mix on high for 2 to 3 minutes until thick and creamy.
If the frosting is too thick, add a splash of milk to thin it out.
When the muffins have cooled completely, use a piping bag with a large open tip to frost them. Enjoy!
Notes
Storage
Refrigerate these muffins for up to 4 days in an airtight container.
For longer storage, wrap chilled muffins in plastic wrap and freeze them for up to a month in an airtight, freezer-safe container.
Defrost frozen muffins overnight. Bring the muffins to room temperature before serving.
General Tips
Mix your muffin batter until combined, but no further. This means that there are no visible dry ingredients. It might be lumpy, and that's okay.
To ensure the most tender muffins, let the batter rest for about 30 minutes so that any gluten can relax.
If you can, measure your flour by weight for the most accuracy.
If measuring by weight isn't an option, loosely spoon your flour into a measuring cup and level it off with a knife. NEVER scoop the flour out directly with the cup. The flour compacts, and you'll use too much.
Be sparing if you need to add milk to thin out the frosting. Remember, you can always add more, but you can't remove it.
Always use fresh baking soda and powder. If they're too old, they won't do the job, and your muffins will be flat.
A Note on Gluten-Free Flour
If you're trying a gluten-free version, use a high-quality 1:1 gluten-free flour. This means the flour already has everything it needs to be used just like regular flour in the same amounts.
Not all gluten-free flours are created equal. We've had the most success with Bob's Red Mill 1:1 baking flour for our baked goods.