1. In a small sauté pan, pour a drizzle of oil and a little butter, add the sliced onions and let them caramelize. Season with salt and add sugar. Set aside.
2. In a bowl, prepare the tartar sauce by mixing mayonnaise and Greek yogurt, add the condiments and parsley. Season to taste. Set aside.
3. In a bowl, place the beef and pork meat, mix with the caramelized onions, spices, and chopped coriander, season with salt and pepper. Shape the patties using a bun-sized cookie cutter or by hand and set aside on a plate.
4. In a hot pan, pour a few drops of oil and a little butter, let it brown, place the patties and let them brown on both sides. Cook to your liking.
5. Finely chop the romaine lettuce leaves. Spread tartar sauce on the burger bun, then add lettuce, the patty, a slice of cheese, thin slices of pickled jalapeños, and pickles. Top with the remaining warm caramelized onions and finally the top of the burger.