200 gm mayonnaise
5 tbsp ketchup
120 gm cornichons, finely chopped
3 tbsp white vinegar
2 tsp onion powder
2 tsp garlic powder
salt to taste

1 tbsp vegetable oil
1 medium white onion, finely chopped
1.35 kg ground beef
12 American cheese slices
6 sesame burger buns
1/2 head iceberg lettuce, thinly sliced
200 gm sliced dill pickles

First make the sauce.
Mix together all of the ingredients.
Season to taste with salt.
Cover and place in the refrigerator until required.

To make the burgers, put the oil in a skillet or frying pan and stir in the onions.
Cook over a medium-low heat, stirring occasionally, until soft and tanslucent.
Turn the heat to medium and continue to cook until golden brown.
Set aside.

Knead the meat lightly with clean hands until soft enough to form patties.
Divide into double the number of burgers required, about 1-cm thick.
Place on a tray layered with parchment paper.
Cover with plastic wrap and refrigerate until ready to cook.

Cook the burgers on a barbecue or under the grill for 1.5 minutes per side for medium rare, 2 minutes per side for medium, or 4 minutes per side for well done.

Melt the cheese over the patties.

Spread the sauce on both sides of the buns.
Place the lettuce and dill pickles on the bottom half of the buns, then flip the burger over so it is cheese side down.
Top with the caramelised onions, the second burger, and the bun top.