01 - Melt butter in a medium saucepan over medium heat. Whisk in flour and cook for 1 minute, stirring constantly to form a smooth roux.
02 - Slowly pour in milk while whisking continuously until smooth. Bring to a gentle simmer and cook for 2-3 minutes until mixture thickens slightly.
03 - Reduce heat to low. Add cheddar and mozzarella cheeses, stirring constantly until completely melted and sauce is smooth.
04 - Stir in garlic powder, onion powder, smoked paprika, pepper, and salt. Taste and adjust seasoning as needed. Serve warm over crispy fries or as a dipping sauce.