Preheat the oven to 375F with the top oven rack positioned in the middle of the oven. Prep a 12-muffin pan with paper liners or generously grease it. If using silicone muffin liners, grease them with spray.
Make the batter:
In a blender, blend the cottage cheese, pumpkin puree, the melted butter cooled butter, eggs, and vanilla extract until smooth.
In a large bowl, mix the flour, sugar, baking powder, salt, and pumpkin spice.
Pour the liquid mixture into the large bowl and use a spatula to mix the batter until there's little to no visible flour left. If you want to add ½ cup chopped walnuts or pecans, fold them into the batter now.
Fill the prepared muffin tin ¾ of the way to the top with batter, then top them off with any remaining batter.
Bake:
Bake in the preheated oven for 22 to 25 minutes, until the tops have browned and a toothpick inserted in the middle comes out clean. Remove them from the oven and let them cool down.
Store:
Once cooled, store them in an airtight container at room temperature (on the counter) for 2 days, in the fridge for up to a week, and frozen for up to 3 months. I recommend warming them up in the microwave for 15 seconds before enjoying them.
Notes
Swap the pumpkin spice for 1 ½ teaspoons cinnamon.