• Preheat the oven to 425°F (220°C). Line a 12-cup muffin pan with paper liners.

Make the Streusel

• Melt the butter over low heat. While the butter is melting place the flour, granulated sugar, brown sugar, cinnamon, and salt in a medium-sized bowl and whisk the ingredients togther. Use your fingers to break up any brown sugar clumps.
• Add the chopped pecans and toss them into the dry ingredients so the nuts are coated with flour. Add the warm melted butter and use a spatula to mix the butter into the dry ingredients until the streusel starts to form clumps. Set the streusel aside until ready to add to the muffins.

Make the Pumpkin Muffins

• Melt the butter in a small saucepan over low heat. When there is just a small piece of butter left, remove the saucepan from the heat. Beat the two eggs together in a small bowl.
• Place the all-purpose flour, baking powder, baking soda, and salt in a medium sized bowl and whisk for 30 seconds to thoroughly combine the ingredients.
 Set the dry ingredients aside.
• Place the brown sugar, granulated sugar, and pumpkin spice in a large bowl and whisk together. Use your fingers to break up any brown sugar clumps. Add the warm melted butter and whisk together until the ingredients are well combined, about 20 seconds. The mixture will have a sandy texture.
• Add the beaten eggs and whisk until the eggs are thoroughly combined and the batter looks smoother and lighter in cooler. Whisk in the pumpkin puree, then whisk in the sour cream.
• NOTE: If you're using leftover pumpkin puree that's been in the refrigerator, bring it room temperature (65-68 degrees F) before adding it to the batter. Adding cold pumpkin puree will cause the batter to curdle and may cause some of the butter to resolidify.
• The batter should be lighter in color and look smooth. Set the batter aside for 10 minutes. Letting the batter sit for 10 minutes will give the sugar more time to thoroughly dissolved.
• Add half of the flour mixture to the wet ingredients. Use a silicone spatula to fold the dry ingredients into the wet ingredients. Add the remaining flour mixture and fold it in until the dry ingredients are thoroughly incorporated, and no white specs of flour remain. Make sure to scrape from the bottom to ensure all the flour is incorporated into the batter.
• The batter may be a little lumpy which is okay. Don’t try to make the batter smooth. That will cause the batter to be overmixed which will result in tough springy muffins.
• Divide the batter between the 12 muffin cups. The batter should almost be the top of each paper liner. If you’re using a kitchen scale, that’s about 80 grams of batter for each muffin cup.
• Divide the streusel evenly between the 12 muffins, about 1/4 cup for each muffin.
• Bake the muffins at 425°F (220°C for 5 minutes, then without opening the oven door reduce the temperature to 350°F (180°C). Bake the muffins for another 15-18 minutes, until the center is done.
• Test for doneness by sticking a toothpick or a cake skewer in the center. There should be no more than 1 or 2 crumbs sticking to the toothpick. For a temperature check, the temperature in the center of the muffin should register 200-203°F using an instant-read thermometer.
• Remove the muffins from the oven and let the muffins cool in the muffin pan for 5 minutes. Place the individual muffins on a wire rack to finish cooling. The muffins can be served warm.

Maple Glaze (Optional)

• Place the powdered sugar in a small bowl. Stir in the maple syrup, then stir in the milk. The glaze should be somewhat thick, but thin enough to drizzle from a spoon.

Storage

• Room Temperature. The muffins can be stored at room temperature in an airtight container for up to 4 days.

  Refrigerator. Store the muffins in airtight container for up to 7 days. You can also wrap each muffin individually in plastic wrap.