Preheat the oven to 350°F. Line a muffin pan. My favorite muffin liners are linked in the blog post above!
Whisk all the wet ingredients together in a medium bowl (1/4 cup melted butter, 3/4 cup pumpkin puree, 1 egg, 1 teaspoon vanilla, 1/4 cup yogurt or sourdough discard and 1/2 cup brown sugar).
Mix all the dry ingredients together in a small bowl (1 cup all purpose, flour, 1/2 teaspoon baking soda, 1 teaspoon baking powder, 1/4 teaspoon kosher salt, 1 teaspoon cinnamon, 1/4 teaspoon nutmeg).
Pour the dry ingredients into the wet mixture, gently mix to combine.
Spoon the batter into the prepared muffin tin, filling each about 3/4th of the way full.
While batter is resting in muffin liners, make the streusel topping. In a small bowl, combine 1/3 cup brown sugar, 1/3 cup oats, 2 tablespoons flour, 3 tablespoons softened butter, 1/2 teaspoon cinnamon. Top each muffin with some streusel topping.
Bake at 350°F for 20 to 25 minutes, or until a toothpick inserted into the center comes out clean.
Enjoy!