1 tablespoon vegetable oil
1 (16 ounce) can crushed pineapple, drained
1 large onion, chopped
1 cup mayonnaise
1 teaspoon vanilla extract
1 (14 ounce) can sweetened condensed milk
Heat oil in a large skillet over medium heat. Saute pineapple with onion for about 10 minutes, stirring. Stir in mayonnaise and vanilla. Cook for about 10 minutes, stirring constantly.
Drain pineapple, reserving juice. Stir juice into pineapple mixture. Return mixture to skillet over medium heat. Cook, stirring frequently, for about 10 minutes, stirring as needed, or until mixture is thickened.
Stir sweetened condensed milk into pot; simmer over medium heat for 5 minutes. Remove from heat. Spoon pineapple mixture into bowl. Spoon mixture into pie dish.