In a large, heavy saucepan melt the butter over medium heat. Add the chopped onion and peppers and sauté until vegetables are soft, about 4 minutes.  Add garlic and sauté for 2 minutes.  Add flour and cook, stirring constantly, for 2 minutes.  Slowly whisk in the stock, milk and heavy cream.  Bring soup to a low boil and reduce heat so that the soup barely simmers.  Cook, stirring frequently, until the soup is very thick and flavorful, about 20 minutes.  Add the grated cheese in ½ cup increments, stirring after each addition until completely melted and smooth.  Do not allow soup to boil.  Season with salt and cayenne pepper to taste.

Serve in shallow bowls, topped with some crumbled crispy bacon bits or a dollop of salsa or crème fraiche, as desired.