Preheat oven to 375℉. Line muffin pan(s) with paper cups. Set aside.
PUMPKIN MUFFINS: In a large bowl, whisk together the oil, sugar, and vanilla. Add the pumpkin puree, eggs, and milk. Whisk until well-combined.
In a separate bowl, stir together the flour, baking soda, baking powder, salt and pumpkin pie spice.
Add the dry ingredients to the wet mixture. Stir until just combined. Fill prepared muffin cups 3/4 full; about 16 muffins.
STREUSEL TOPPING: Melt the butter in a medium-size microwave safe bowl in the microwave for 30-60 seconds, until just melted.
Add the flour, sugar, brown sugar, and pumpkin pie spice. Mix with a fork until combined. TIP:Try and keep the crumbs somewhat small. The bigger pieces tend to fall off more easily after baking.
Spoon the streusel on top of the pumpkin batter and press gently into the batter so that it sticks.
Bake at 375℉ for 18-20 minutes or until a toothpick inserted in the center comes out with just a few moist crumbs. Do not over-bake. Cool completely.
Notes
Store muffins in an airtight container for up to 3 days at room temperature. Alternately wrap cooled muffins individually with plastic wrap and place inside a freezer safe bag. Freeze for up to 3 months.