Crumb-topped Pumpkin Pie

This will be this year's version of Thanksgiving pumpkin pie. I saw a couple of similar recipes for this online, and just tried to combine them into this. I actually made this a week or two ahead of time and froze it, so we'll see how well it holds up!

Ingredients
1 (15 ounce) can pumpkin puree
1 (14 ounce) can sweetened condensed milk (I used fat-free)
2 eggs
1 teaspoon ground cinnamon (I increased this a touch)
1/2 teaspoon ground ginger
1/2 teaspoon ground nutmeg
1/2 teaspoon salt
1 (9 inch) unbaked pie shell

2 tablespoons all-purpose flour
1/4 cup packed brown sugar
1 teaspoon ground cinnamon
2 tablespoons butter, chilled
1/2 cup chopped walnuts

Directions
Preheat the oven to 425 degrees F (400 for altitude).
In a large bowl, mix together the pumpkin, sweetened condensed milk, and eggs. Stir in 1 teaspoon cinnamon, ginger, nutmeg, and salt. Pour filling into pie shell.
Bake for 15 minutes in the preheated oven. While the pie is baking, prepare the streusel topping: In a small bowl, combine the flour, brown sugar, and 1 teaspoon cinnamon. Blend in the cold butter with a fork or pastry blender until the mixture is crumbly. Mix in the chopped nuts. Sprinkle the topping over the pie.
Reduce the heat to 350 degrees F (325 for altitude). Bake an additional 40 minutes, or until set.