In a small bowl, whisk together sugar, cinnamon, salt, and flour.
Add cooled, melted butter and stir until crumbs form.
Muffins
Preheat the oven to 350 °F. Use convection option if available with your oven.
In a large mixing bowl, whisk together the dry ingredients: flour, baking powder, baking soda, salt and spices.
In another bowl beat eggs until frothy. Add brown sugar, pumpkin puree, vanilla, oil and sour cream. Gradually fold the egg mixture into the flour mixture, until just combined.
Using a cookie scoop transfer batter to muffins tins or silicon baking cups. The cups will be least ¾ full of batter.
Sprinkle the crumb topping equally on the muffins
Bake muffins for 25 minutes OR until a toothpick inserted in the center comes out clean.