Emily's Streusel-Topped Pumpkin Pie

Emily's Streusel-Topped Pumpkin Pie
(from condensed milk label)

1 (15 oz) can pumpkin
1 (14 oz) can sweetened condensed milk
1 egg
3/4 tsp. cinnamon
1/2 tsp. each ginger, nutmeg, salt

Topping:
1/4 c. brown sugar
1/2 tsp. cinnamon
2 Tbsp. flour
2 Tbsp. cold butter
3/4 c. walnuts

Beat pumpkin, milk, egg, spices and salt with wire whisk. Pour into unbaked pie shell. Bake 15 minutes at 425F. Combine topping ingredients -- cut in butter until crumbly. Sprinkle streusel topping over pie. Bake at 350F for an additional 40 minutes or until set.