Pumpkin Streusel Pie

1 (15 ounce) can pumpkin puree 1 (14 ounce) can sweetened condensed milk 2 egg yolks 1 teaspoon ground cinnamon 1/2 teaspoon ground ginger 1/2 teaspoon ground nutmeg 1/2 teaspoon salt 2 egg whites 2 (9 inch) unbaked pie shells 2 tablespoons all-purpose flour 1/4 cup packed brown sugar 1 teaspoon ground cinnamon 2 tablespoons butter, chilled 1 cup chopped walnuts or pecans


 * Preheat the oven to 425 F (220 C/gas mark 7).


 * In a large bowl, mix together the pumpkin, sweetened condensed milk, and egg yolks. Stir in cinnamon, ginger, nutmeg, and salt. In a large glass or metal bowl, whip egg whites until soft peaks form. Gently fold into pumpkin mixture. Pour filling into pie shells.


 * Bake for 15 minutes in the preheated oven. While the pies are baking, prepare the streusel topping: In a small bowl, combine the flour, brown sugar, and 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 pies.


 * Reduce the heat to 350 F (175 C/gas mark 4). Bake an additional 40 minutes, or until set.