In a bowl, mix the sugar and peanut butter together using a fork until mixture looks like coarse crumbs. Remove 1/2 cup crumbs and set aside. Spread the rest of the crumbs in the baked pie shell. Mix together 2 tablespoons margarine, evaporated milk, salt, the 3 egg yolks (keep the whites for the meringue), 1/4 cup cornstarch, 1/2 cup sugar and 1 teaspoon vanilla in a pan. Cook on medium heat on top of the stove stirring constantly until thickens. (about 5 to 7 minutes). I remove as soon as it starts to thicken. (This will burn easily so watch it closely).