1. In a skillet, melt the butter. Add the onion, cover and cook
over moderately low heat, stirring, until softened, 15 minutes.
Uncover and cook over moderate heat, stirring, until the onion
is caramelized, 20 minutes; add water if necessary to keep the
onion from burning. Season with salt and pepper.
2. In a small bowl, whisk the mayonnaise with the lemon juice,
garlic, paprika and cayenne. In a steady stream, whisk in the olive
oil and season with salt and pepper. Fold in the cornichons and
3. Heat a griddle. In a bowl, mix the Gruyére and cheddar.
Season the beef patties with salt and pepper and cook over high
heat for 2 minutes. Flip the burgers and top with the mixed
cheeses. Carefully cover the burgers with a large inverted roasting
pan and cook for 2 minutes longer, until medium-rare and the
cheese is melted.
4. Spread the paprika mayonnaise on the bottom halves of the
buns and stack 2 patties on each. Top with the onions, pickles and
lettuce and serve. —Ron Boyd