In a medium bowl, stir together the flour, brown sugar, and granulated sugar. Using a pastry blender, cut in the cold butter pieces until the mixture resembles fine crumbs. Stir in the nuts.
Set aside 1 cup of the crumb mixture. Firmly press the remaining crumb mix over the bottom and halfway up the sides of a 2-quart rectangular baking dish; set aside.
In a large bowl, stir together the pumpkin, condensed milk, beaten eggs, cinnamon, allspice and salt until well mixed. Pour the mixture into the prepared baking dish. Sprinkle with the reserved crumb mixture.
Bake in a 350 degree oven about 55 minutes or until the topping is golden brown and the filling is set; cool.