01 - Melt butter in a medium saucepan over medium heat. Whisk in flour and cook for 1 minute, stirring constantly, until a smooth paste forms.
02 - Slowly pour in milk while whisking continuously to prevent lumps. Bring to a gentle simmer and cook for 2–3 minutes until mixture slightly thickens.
03 - Reduce heat to low. Add cheddar and mozzarella cheeses gradually, stirring constantly until completely melted and sauce becomes smooth and creamy.
04 - Stir in garlic powder, onion powder, smoked paprika, black pepper, and salt until fully incorporated. Taste and adjust seasoning as desired.
05 - Serve immediately over crispy fries or as a warm dipping sauce. Keep warm on low heat if needed, stirring occasionally to prevent skin formation.