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