Oven Creamed Potatoes

6 lg potatoes, cooked and diced
1/4 cup butter
1/3 cup flour
3/4 tsp salt
1/4 tsp mustard
1/4 tsp black pepper
2 cans evaporated milk
2 cups grated cheese (I use sharp cheddar)

in a saucepan, over very low heat, melt butter and stir in flour, salt, pepper and mustard.
Slowly add milka little at a time and cook, stirring constantly until it thickens.
Pour mixture into casserole dish then layer potatoes on top. Sprinkle cheese over potatoes. I usually add a little extra salt and pepper over the potatoes before adding the cheese. Ive also added crispy chopped bacon over the potatoes. this is so delicious..and a sure hit with kids!