Preheatoven to broil. Set rack to middle-high level in oven.
Add 2 Tablespoons butter, 2 Tablespoons flour to a saucepan over medium heat. Whisk together melted butter and flour for 1-2 minutes, until paste forms.
Add 1/2 cup milk to butter and flour paste, whisk until smooth. Constantly whisk until thickened, about 2-3 minutes.
Once milk sauce is thickened, add in 2 cups shredded cheese, 1/4 teaspoon kosher salt. Whisk until cheese is melted. Sauce will be thick.
Add in 2/3-1 can salsa. Adding lots of salsa might break up cheese sauce. Whisk together. Cook for about a minute, if sauce is too thick, add 1 Tablespoon of milk at a time, until desired thickness. It should be easy to pour over chips.
Spread an even layer of chips onto baking sheet. It’s ok if there are spots with 2 layers of chips.
Evenly pour fire roasted salsa queso over chips. Then distribute protein, corn, vegetables if desired.
Place in oven for 2-5 minutes, until chips barely start to brown. Check frequently to avoid burning chips.
Add desired fresh toppings to cooked nachos, like sour cream, green onion, guacamole/avocado, diced tomatoes, etc. Add additional salsa, if desired. Enjoy immediately!