Prep Time: 30 minutes
Cooking Time: 30 minutes
DirectionsPreheat oven to 350 degrees F.
Melt butter in a saucepan over medium heat. Cook onion in melted butter for 5 minutes, or until tender. Stir in flour, salt, and pepper. Slowly add milk and cook, stirring occasionally, until thickened, 7 to 10 minutes.
Remove milk mixture from heat. Add 1 1/2 cups cheese and stir until cheese is melted.
Combine cheese sauce with cooked macaroni and green chiles. Mix well. Transfer to a 1 1/2-quart casserole dish and top with remaining cheese. Bake 30 minutes or until the cheese is bubbly and lightly browned.