Ingredients

6 potatoes
4 tbsp butter
3 tbsp flour
1 tsp salt
1/4 tsp pepper
2 1/2 c. milk
1 small onion

How to make it

1. You need to preheat oven to 350ºF.
2. You need to peel and cut the potatoes into thin slices. 
3. Heat 3 tbps of butter in a saucepan over low heat until melted.
4. Mix in flour, salt and pepper. 
5. Cook over low heat, so that the mixture is smooth and bubbly. 
6. Then, gradually stir in milk,  slowly add 1/2 cup at a time.
7. Heat it so that it begins to boil. 
8. Stir for about 1 minute.
9. Arrange potatoes in greased casserole in 3 layers,
10. Each layer shuold have some chopped onions and 1/3 of the sauce. 
11. Put the top with the remaining 1 tablespoon of butter, broken into little pieces.
12. Cover and bake until potatoes are tender, so about 60-70 minutes. 
13. Leave it for 5 to 10 minute before serving.

Enjoy!