Step 1: Slice 1 medium onion. Shred and combine a ½ cup each of Monterey Jack, Oaxaca, Chihuahua, and white cheddar cheeses.
Step 2: Heat a large saucepot over medium heat and slowly caramelize the onions. Add ½ cup roasted garlic and 8 cups milk. Bring to a boil; stir to avoid scalding the milk.
Step 3: In a separate saucepot, melt ¼ pound butter. Add 1 cup flour and stir to make a roux that’s slightly golden and nutty-smelling. Slowly add the onion, garlic, and milk mixture until it thickens slightly. Stir in shredded cheese and 1 cup canned nacho cheese. Once melted, run sauce through a fine-mesh strainer. Season, add your favorite toppings, and serve with tortilla chips.
—Illustrations by Peter James Field