Double Cheddar Beef Smash Burgers with Lime Avocado

Steps

1. Prep first: slice the tomato and red onion, and cut the cheddar into 8 pieces. Divide the beef into 8 loose balls without packing them; keep cold.
2. In a bowl, mash the avocado with the lime juice and a quarter of the salt until chunky.
3. Stir together the remaining three quarters of the salt, the black pepper, garlic powder and smoked paprika for the seasoning.
4. Heat a large cast-iron skillet over medium-high heat. Toast the bread slices in the dry skillet until golden, about 1 minute per side, then set aside.
5. Brush the hot skillet with the canola oil. Add 4 beef balls, smash each very thin with a sturdy spatula, and sprinkle with half of the seasoning.
6. Cook until the edges are deeply browned and crisp, about 2 minutes, then scrape and flip. Top each with a piece of cheddar and cook 1 minute more, until the cheese melts and the beef reaches 160°F (71°C). Transfer to a plate.
7. Repeat with the remaining 4 beef balls, the remaining half of the seasoning and the remaining cheddar.
8. Spread the mustard on 4 toasted bread slices. Stack two cheesy patties on each, then top with the red onion, tomato and lime avocado.
9. Close with the remaining 4 bread slices and serve right away.