Preheat oven to 350 degrees F. Line a 12-cup muffin pan with paper liners and lightly spray the liners with nonstick cooking spray. If you don't have liners, grease the pan with nonstick cooking spray. Set aside.
In a small bowl, combine the sugar, flour, and melted butter. Stir until moistened. Set aside while you make the muffin batter.
In a medium bowl, whisk together flour, spices, baking soda, and salt. Set aside.
In a large bowl, combine the pumpkin, sugars, oil, buttermilk, eggs, and vanilla extract. Use a spatula to stir until the ingredients are smooth.
Gradually add the dry ingredients to the pumpkin mixture and stir until just combined.
Gently fold in ¾ cup of the chocolate chips. Don’t over mix.
Divide the batter among muffin cups, filling each cup 3/4 full. Top each muffin with streusel topping. Sprinkle the remaining chocolate chips over the streusel.
Bake the muffins for 24-28 minutes or until muffins are set and a toothpick stuck in the middle of a muffin comes out clean.
Let the muffins cool to room temperature and enjoy!
The muffins will keep covered on the counter for up to 3 days. The muffins can also be frozen for up to 2 months.