Le Burger

• for the burgers
• 1/2 red onion, minced
• 1 tablespoon butter
• kosher salt + freshly ground pepper
• 1/4 cup cornichons
• 1 anchovy filet
• 1 tablespoon capers
• 1 pound ground chuck or sirloin
• 4 slices bacon (I like applewood smoked)
• Gruyere cheese, shaved finely (a vegetable peeler woks great)
• 4 burger buns
• iceberg lettuce, shredded
• for the ketchup
• 1/2 red onion, minced
• 2 tablespoons olive oil
• kosher salt
• 1 tablespoon tomato paste
• 1 can tomatoes, or 1/2 of a big one, preferably San Marzano
• 2 teaspoons sherry vinegar
• 1 teaspoon sugar

1. First, make the ketchup: Saute 1/2 of the red onion in the olive oil over medium heat until completely wilted and lightly golden, about 10 minutes, seasoning well with salt during cooking. Add the tomato paste, stir well, and let cook for an additional 2 minutes. Add the tomatoes, sherry vinegar, sugar, and season with a bit more salt. Bring to a boil and then let simmer happily until quite thick, about 20 minutes. Stir from time to time, scraping up the crud that forms on the bottom of the pan. When done, let cool, run through a food processor, taste, and adjust seasoning. You might like a little more vinegar or sugar.
2. Then prepare the burgers: Saute the other 1/2 of that red onion over medium heat in the butter until very soft and translucent, about 7 minutes. Season with salt and pepper early in cooking. When finished, remove pan from heat and leave to cool.
3. Rinse the cornichons, anchovy, and capers well. Transfer them to your food processor (after you've made the ketchup and cleaned the food processor, that is), scrape in the sauteed onion, and process. The mixture will be an unattractive greenish-yellow. Transfer to a large bowl. Grind over quite a bit of pepper, and add 1/2 tsp kosher salt. Add the ground meat, and mix well but lightly, trying not to compact the meat too much. Roll into 4 balls, and then press down lightly to make a patty, making a little well in the center with your thumb. Make sure everything is at room temperature before cooking.
4. Fry the bacon in whatever pan you will cook the burgers, turning once or twice. (Cast iron is nice if you have it.) When it is done to your liking, remove the bacon and set on paper towels to drain. Then cook the hamburgers in the bacon fat over high heat for about 5 minutes for medium, 3 minutes on the first side and 2 on the second. Put the cheese on top of the burgers while they are cooking on the second side. Cover the burgers for the last minute of cooking so that the cheese melts fully. Then remove to a plate and let rest.
5. Toast the burger buns, and break the bacon into pieces. To serve, I like to put the bacon down first, then the burger + cheese, then the lettuce. Spread the top bun with your fancy ketchup. Bon appetit!

burgers, red onion, butter, kosher salt , cornichons, anchovy filet, capers, ground chuck, bacon, gruyere cheese, buns, ketchup, red onion, olive oil, kosher salt, tomato paste, tomatoes, sherry vinegar, sugar

Taken from food52.com/recipes/5854-le-burger (may not work)