SHERRY THORUP. . . SWEET POTATO PIE

 
 
1 1/2 cup fresh (cooked) or canned sweet potatoes or yams
1/2 cup sugar
1 teaspoon cinnamon
1 teaspoon allspice
1/2 teaspoon salt
2 eggs, beaten
1 cup evaporated milk
2 Tablespoons butter, very soft
1 9-inch unbaked