Start by preparing the burger sauce and slicing the croissants. Keep the croissants intact as much as possible so they hold the juicy patties and toppings without falling apart.

1. Make the burger sauce.In a small bowl, combine the mayonnaise, ketchup, mustard, pickle juice, smoked paprika, garlic powder, and a pinch of black pepper. Stir until smooth, then refrigerate while preparing the burgers.
2. Divide the beef.Gently divide the ground beef into 8 equal portions, about 2 ounces each. Roll each portion into a loose ball without compacting the meat too much. This helps create tender patties with crispy edges.
3. Prepare the croissants.Slice each croissant horizontally using a serrated knife. Set the tops and bottoms aside. If desired, warm the cut sides briefly in a dry skillet over medium-low heat to give them a light golden color.
4. Heat the skillet.Place a large cast-iron skillet or heavy frying pan over medium-high heat until very hot. Add a thin layer of oil if the pan is not well seasoned.
5. Smash the patties.Place a beef ball in the hot skillet and immediately press it flat using a sturdy spatula or burger press lined with parchment paper. Aim for a thin patty with uneven, crispy edges. Repeat with the remaining portions, working in batches if necessary.
6. Season and sear.Sprinkle the patties with salt, black pepper, and garlic powder. Cook for about 2–3 minutes without moving them, until the edges are deeply browned and crispy.
7. Flip and add cheese.Scrape beneath each patty to preserve the browned crust, then flip. Cook for another 1–2 minutes, or until the beef reaches a safe internal temperature of 160°F (71°C). Place a slice of cheese on four patties during the final minute and allow it to melt. Stack a second patty on each cheesy patty for a double smash burger.
8. Assemble the burgers.Spread the prepared burger sauce over the bottom half of each croissant. Add lettuce, tomato, and pickle slices, then place a double patty on top. Add sliced onion if desired and finish with the croissant top.
9. Serve immediately.Arrange the burgers on a serving platter and enjoy while the patties are hot, the cheese is melted, and the croissants are still flaky. Serve with French fries, potato wedges, or a simple side salad.