Preheat your oven to 400 degrees Fahrenheit. While the oven is heating up, prepare your muffin tins by spraying them with cooking spray or lining 18 muffin cups with paper liners.
In a large mixing bowl, combine 2 1/4 cups all-purpose flour, 3/4 cup old-fashioned oats, 2 teaspoons baking soda, 1 teaspoon baking powder, 1 teaspoon salt, and 3 teaspoons pumpkin pie spice. Use a whisk to mix everything together until well combined, ensuring there are no lumps.
In a separate mixing bowl, whisk together 1 1/2 cups pumpkin puree, 1 1/4 cups brown sugar, 2/3 cup oil, 1/2 cup applesauce, 3 large eggs, and 2 teaspoons vanilla extract. Mix until everything is well blended and smooth.
Next, carefully add the dry ingredients from the first bowl into the wet ingredients. Gently stir together just until combined; be careful not to overmix, as this can lead to dense muffins.
Using a spoon or an ice cream scoop, fill the muffin cups about 3/4 of the way full with the batter. This will allow room for the muffins to rise.
In a small bowl, prepare the streusel topping by combining 1/4 cup rolled oats, 1/4 cup all-purpose flour, 1/4 cup brown sugar, and 1/2 teaspoon cinnamon. Stir this mixture together, then add 2 tablespoons butter, mixing until small clumps start to form.
Sprinkle the streusel topping generously over the muffin batter in each cup, ensuring each muffin gets a nice coating.
Place the muffin tin in the preheated oven and bake for 8 minutes at 400 degrees. After 8 minutes, reduce the temperature to 350 degrees and continue baking for an additional 10 to 15 minutes. You’ll know the muffins are done when a toothpick inserted into the center comes out clean.
Once baked, remove the muffins from the oven and allow them to cool in the tin for a few minutes. Then, transfer them to a cooling rack to cool completely.
Enjoy your freshly baked muffins warm, or store them for later! These muffins are perfect for breakfast, snacks, or even dessert.
