• Preheat the oven to 350 F. Line a muffin tin (for 12 large muffins) with parchment paper baking cups (link in comments).

Make the streusel topping:

• Finely chop the pecans for the topping. Add the brown sugar, flour, pecans, cinnamon, & salt to a medium bowl. Set aside.
  
• Brown butter in a small sauce pan over medium heat. Cook for 3-5 minutes until the color turns to a medium brown, deep caramel tone & it smells sweet like butterscotch.
• Carefully add the butter to the bowl with the other ingredients; try to keep any solids in the bottom of the pan. Wipe the pan out with a paper towel & set aside to use again. Mix ingredients until well combined & then set aside.
  

Make the muffins:

• First mix all dry ingredients together: flour, baking soda, baking powder, salt, & spices.
  
• Then mix the wet ingredients ... put the brown sugar in a large mixing bowl. Brown the butter in the same pan as before. Once ready, pour into the large mixing bowl & beat together with the sugar, using an electric mixer.
  
• Add one egg at a time, beating the mixture on low for 2-3 minutes after each egg.
  
• Add the pumpkin puree & beat for 2-3 minutes.
  
• Slowly add the dry ingredients to the pumpkin mix, beating on low. Mix until just combined, using a rubber spatula to wipe down the sides as needed.
  
• Add the chopped pecans & dark chocolate (if using) & gently fold them in with the spatula.
  
• Using 2 large spoons, drop the muffin mix into the muffin liners. Use all of the mixture, filling the cups to the top.
  
• Using a large spoon & your fingers, add the streusel topping to the muffins. Gently push the topping into the muffin batter, getting as much as possible to stick on well.
  
• Bake the muffins for 35 minutes, until a toothpick or knife comes out clean.
• Let cool in the muffin tin for 5 minutes before moving to a cooling rack. Once they are cool enough to eat...
• Enjoy!