Lemon Sponge Pie
["1 c. sugar", "3 eggs, separated", "juice and rind of 1 lemon", "1/2 tsp. salt", "2 Tbsp. flour", "1 1/2 c. milk, heated", "2 Tbsp. butter", "1 (9-inch) pie crust"]
["Cream butter and sugar.", "Add egg yolks; beat well.", "Add milk, flour, salt, lemon juice and grated rind.", "Fold in stiffly beaten egg whites.", "Bake at 375\u00b0 until set, about 35 minutes."]
["sugar", "eggs", "lemon", "salt", "flour", "milk", "butter", "crust"]