Cheesy Potatoes

Bahan-bahan (8 porsi)

• 2 lb potatoes
• 3 tbsp butter
• 3 tbsp all purpose flour
• 1 tsp garlic powder
• 1 tsp onion powder
• 1/2 tsp dry mustard powder
• 2 cup milk
• 2 cup shredded cheese (divided)
• 1 cup sour cream