Preheat oven to 425.
In a large bowl, beat the eggs.
Add pumpkin, sugar and 2 1/2 teaspoons of pumpkin spice. Beat to combine.
Gradually mix in evaporated milk.
Grease a 10" cast iron skillet.
Place pie crust in skillet.
Pour in pumpkin mixture to just below top of crust.
Bake at 425 for 15 minutes.
Reduce to 350 and bake for an additional 30.
In a medium bowl, combine butter, flour, brown sugar and 1/2 teaspoon of pumpkin pie spice.
Use a pastry cutter or a fork to cut butter into dry ingredients until crumble forms.
Sprinkle streusel evenly over pie top.
Use aluminum foil to cover the edges of the pie crust.
Bake another 30 minutes.
Cool for 2 hours before cutting.