Pennsylvania Dutch Apple Salad

2 tablespoons flour
1 tablespoon granulated sugar
1 egg, beaten
1 cup milk
4 large apples, chopped
1/2 cup celery, chopped
1/2 cup walnuts, chopped

Cook flour, sugar, egg, and milk in a small saucepan over medium heat until thick, stirring constantly. Remove from heat and cool completely. Pour over apples, celery, and walnuts in a large serving bowl. Toss lightly to coat. Chill.