1. In a medium sauce pan melt butter.
2. Meanwhile, in small bowl, add flour to milk. Stir until there are NO lumps in milk. Add salt, pepper and onion powder to taste.
3. When butter is melted add milk mixture. When it starts to bubble remove from heat.
4. Add cheese and potatoes. Stir until cheese has melted.
5. Transfer to medium casarole dish and bake @ 350 for 30 - 40 min until top starts to turn brown.