Bunless Smash Burgers with Quick Pickles

Steps

1. Make the quick pickles first: stir the cider vinegar, water and sugar in a bowl until the sugar dissolves, then add the cucumber and dill and set aside for at least 20 minutes.
2. Put the whole red potatoes in a pot, cover with water from the tap (not counted), boil 15 to 18 minutes until tender, then drain.
3. Heat half the olive oil in a large cast-iron skillet over medium-high heat. Press each potato flat with a glass, fry 4 to 5 minutes per side until crisp, season with a pinch from one quarter of the salt, then move to a plate and keep warm.
4. Wipe the skillet and heat the remaining olive oil over high heat until it shimmers.
5. Working in batches, add the beef balls, top each with a few slices of the onion, and smash them hard and thin with a sturdy spatula. Season with the remaining salt and the black pepper.
6. Cook about 2 minutes until the edges are deeply browned and crisp, flip so the onion sears underneath, and cook 1 more minute until the patties reach 160°F (71°C).
7. Lay the romaine leaves on plates and stack two patties on each. Spread the mustard over the patties, then top with the tomato and the drained pickles.
8. Serve the burgers with the crispy smashed potatoes on the side.