Walnut Pumpkin Pie

1 (6 oz.) Graham Cracker Pie Crust
1 (15 oz.) can pumpkin
1 (14 oz.) Sweetened Condensed Milk (NOT Evaporated)
1 Egg
1-1/4 tsp. ground cinnamon
1/2 tsp. ground ginger
1/2 tsp. nutmeg
1/2 tsp. salt
1/4 cup packed brown sugar
2 Tbs. flour
2 Tbs. cold margarine or butter
3/4 cup chopped walnuts

Heat oven to 425 degrees F.  In mixing bowl, combine pumpkin, sweetened condensed milk, egg, 3/4 tsp. cinnamon, ginger, nutmeg and salt; mix well.  Turn into pie crust. Bake 15 minutes; remove pie.  Reduce oven temperature to 350.  In small bowl, combine sugar, flour and remaining 1/2 tsp. cinnamon; cut in margarine until crumbly.  Stir in walnuts.  Sprinkle walnut mixture evenly over pie.  Bake 40 minutes or until knife inserted 1 inch from edge comes out clean. Cool.  Garnish as desired.  Cool Whip tastes great on this pie!