01 - Melt butter in a medium saucepan over medium heat. Whisk in flour and cook for 1 minute until bubbling but not browned, creating a smooth roux.
02 - Slowly pour in milk while whisking constantly to eliminate lumps. Continue cooking and whisking for 3-4 minutes until mixture thickens and coats the back of a spoon.
03 - Reduce heat to low. Stir in cubed cream cheese until fully melted and incorporated into the base.
04 - Gradually add shredded cheddar and mozzarella cheeses, stirring continuously until completely melted and the sauce is smooth and velvety.
05 - Mix in garlic powder, onion powder, smoked paprika, salt, black pepper, and Dijon mustard until well combined. Remove from heat immediately and serve with warm pretzels.