To make lactose-free, sugar free, sweetened condensed milk, combine cold water and milk powder and stir to make a paste. Cover and microwave on HIGH for 45 to 60 seconds or until mixture is hot but not boiling. Stir in your choice of sweetener. Cover and refrigerate for at least 2 hours before using.
Preheat the oven to 425 degrees F (220 degrees C).
In a large bowl, mix together the pumpkin, sweetened milk mixture and egg yolks. Stir in 1 teaspoon 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 shell.
Bake for 15 minutes in the preheated oven then reduce the heat to 350 degrees F (175 degrees C). Bake an additional 40 minutes, or until set.
While baking, prepare the topping by combining the remaining sweetener, molasses, and a drop of rum extract (butterscotch or maple is also fine). Combine using a fork until evenly blended. Add the flour and cinnamon, then blend in the cold butter until the mixture is crumbly. Mix in the chopped nuts.
Sprinkle the sweet nut topping over the pie about 15 minutes before it's done baking.
