In a medium bowl, whisk together the ½ cup all-purpose flour, ⅓ cup packed brown sugar, ¼ cup granulated sugar, and ½ teaspoon ground cinnamon.

Add the ¼ cup cold unsalted butter to the bowl. Cut the butter into the dry ingredients until the mixture resembles coarse crumbs.

Stir in the ½ cup chopped pecans or walnuts, if using.

Place the streusel topping in the refrigerator while you prepare the muffin batter.

Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease the tin.

In a large bowl, whisk together the dry ingredients: 2 cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon ground cinnamon, ½ teaspoon ground nutmeg, ¼ teaspoon ground cloves, and ½ teaspoon salt.

In a separate large bowl, whisk together the wet ingredients: 1 ½ cups granulated sugar, 1 cup pumpkin puree, ½ cup vegetable oil, 2 large eggs, and 1 teaspoon vanilla extract.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fill each muffin cup about ⅔ full with the pumpkin muffin batter.

Remove the streusel topping from the refrigerator and sprinkle generously over the top of each muffin.

Bake in the preheated oven for 18-22 minutes, or until a skewer inserted comes out clean.

Let the muffins cool in the muffin tin for a few minutes before transferring them to a wire rack.