Now that you have your ingredients ready, let’s bring these muffins to life. Follow these steps for a delightful baking experience:

1. Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners or grease it lightly.
2. In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Set aside.
3. In a large bowl, combine the melted butter, granulated sugar, and brown sugar. Whisk until smooth.
4. Add the eggs, one at a time, mixing well after each addition. Stir in the pumpkin puree and vanilla extract.
5. Gradually add the dry ingredients to the wet ingredients, stirring gently until just combined. Be careful not to overmix.
6. Fold in the diced apples, ensuring they are evenly distributed throughout the batter.
7. For the streusel topping, mix the flour, granulated sugar, brown sugar, and cinnamon in a small bowl. Add the melted butter and combine until the mixture resembles coarse crumbs.
8. Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full. Sprinkle the streusel topping generously over each muffin.
9. Bake for 18-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
10. Allow the muffins to cool in the pan for about 5 minutes before transferring them to a wire rack to cool completely.