-nondairy Whipped topping; thaw Pecans; chop For crust, combine crushed crackers, melted margarine, and granulated sugar; toss to mix well. Spread evenly into a 9-inch pie plate, pressing onto the bottom and up the sides to form a firm, even crust. Chill about 1 hour or freeze 20 minutes, or till firm. Meanwhile, for rum sauce, mix brown sugar and cornstarch in a small saucepan. Stir in water. Stir in evaporated milk and corn syrup. Cook and stir over medium heat till thickened and bubbly (mixture may appear curdled). Cook and stir 2 minutes more. Remove from heat; stir in the 1 tablespoon margarine or butter and the rum. Set aside to cool. Stir together pumpkin and pumpkin pie spice in a large mixing bowl. Fold in ice cream and the 4-ounce container thawed whipped topping. Pour half of the pumpkin mixture into prepared crust. Reserve 2 tablespoons sauce for top of pie. Pour remaining sauce evenly over pumpkin layer, marbling slightly. Top with remaining pumpkin mixture. Drizzle with reserved sauce. Cover and freeze at least 4 hours or till firm. To serve, let stand at room temperature for 15 to 30 minutes. Dollop with whipped topping and sprinkle with chopped pecans. Makes 8 servings.