Preheat the oven to 350°F. Place the shredded cheeses in a bowl and mix until well combined. Set aside.
Add oil to a medium-sized cast-iron skillet over medium-high heat. Once oil is hot, add the chorizo. Cook, breaking apart the meat into crumbles as it cooks, until cooked through, about 8 to 10 minutes.
Add the onions and garlic. Sauté for 5 to 6 minutes, until the onion is soft and translucent.
Use the spatula or a spoon to remove 1/2 of the chorizo mixture from the skillet. Set it aside.
Sprinkle in 3/4 of the cheese mixture. Press it down gently. Then add half of the reserved chorizo and top it with the remaining cheese mixture.
Bake for 15 to 20 minutes, until melty. Carefully remove it from the oven and top with the remaining chorizo. Serve with corn chips or tortillas, as desired.
Storage: Queso fundido is best when freshly made. However, you can refrigerate any leftovers in an airtight container for up to 4 days. You can also keep it in the skillet you made it in if you cover it tightly with foil.Reheat: To reheat it, microwave it in 15-second intervals until nice and melty. You can also re-heat it in the oven at 350°F for 8 to 12 minutes, until warmed through.Serving: Queso fundido con chorizo is best with Tortilla Chips for a quick appetizer. For a healthier alternative, serve it with my Air Fryer Tortilla Chips. You can also serve it with warm Corn Tortillas, or Flour Tortillas, for a cheesy taco/burrito bite.Spicy: Use spicy chorizo, or add 1/2 finely chopped serrano peppers, to the chorizo mixture as it cooks. This will give the recipe a good kick of heat.Chilorio: Use one part chorizo and one part chilorio, or substitute it altogether, to give this appetizer a new spicy, smokey dimension.Cheese: Chihuahua and Manchego are great because they’re more savory, but queso asadero and even adobera cheese make great swaps.