Preheat oven to 400ºF.
Heat butter in a saucepan, add onions, garlic, chili pepper and stir 2-3 minutes. Add flour and stir 1 minute. Whisk in milk and thicken; stir in Monterey Jack and Parm cheeses.
Arrange a layer of potato chips on a baking sheet, top with cheese sauce and blue cheese crumbles. Place in oven and bake until cheese melts and the edges are brown.
Serve on a platter or in shallow bowls topped with hot sauce and finely chopped carrot, celery and onion.