• Preheat the oven to 350°F (176°C), and line a muffin tin with paper or reusable liners. Then, melt butter, and allow to cool, around 10 minutes and set both aside.
• In a medium mixing bowl, whisk together AP flour, baking powder, baking soda, salt and pumpkin pie spice, mix until combined.
• Add melted and cooled butter, brown sugar, white granulated sugar, eggs, pumpkin puree, sour cream or plain greek yogurt, pure vanilla extract, and mix together until the dry ingredients are moistened (around 10-12 turns if mixing by hand).
• Equally divide batter into prepared muffin liners. Bake for 20 to 25 minutes until muffins are golden, and toothpick comes out clean when poked into the middle. When muffins done, remove from oven and allow to cool in pan. Serve, and enjoy. Keep leftovers in an airtight storage container lined with paper towels.
• If frosting, allow muffins to completely cool, then frost, and serve.

Cream Cheese Frosting

• Beat the cream cheese and butter together on high speed until smooth and creamy. Start slow to avoid splatter.
• Add 2 cups confectioners sugar (3 cups if needed, taste frosting before adding, I usually only use 2 cups), vanilla and salt. Mix on low speed for 30 seconds or until most of the sugar combined, then switch to high speed for an additional minute or until all ingredients incorporated.
• Add to muffins, and store leftovers covered in refrigerator in an airtight storage container for up to 5 days, or freeze for up to 3 months.