Creamy Au Gratin Potatoes

INGREDIENTS

• 4 russet potatoes, sliced into 1/4 inch slices
• 1 onion, sliced into rings
• salt and pepper to taste
• 3 tablespoons butter
• 3 tablespoons all-purpose flour
• 1/2 teaspoon salt
• 2 cups milk
• 1 1/2 cups shredded Cheddar cheese