Vincente's Macaroni and Cheese

Ingredients (9)

• + 1 (8 ounce) box elbow macaroni add to pantry
• + 1 tablespoon butter add to pantry
• + 1 small onion, chopped add to pantry
• + 2 tablespoons all-purpose flour add to pantry
• + 1 teaspoon dry mustard add to pantry
• ✓ ¼ teaspoon salt
• + 1 cup milk add to pantry
• + 1 ½ cups grated sharp Cheddar cheese add to pantry
• + 1 pinch ground black pepper add to pantry