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 slightly thickened.
03 - Reduce heat to low. Add cheddar and mozzarella cheeses, stirring until completely melted and incorporated into a smooth sauce.
04 - Stir in garlic powder, onion powder, smoked paprika, black pepper, and salt. Taste and adjust seasoning as needed. Serve warm over fries or as a dipping sauce.