Wash and dry all produce. Preheat oven to 425 degrees. Halve, peel, and thinly slice onion. Slice tomato into rounds. Split buns in half. Shape beef into two evenly sized patties (make them slightly wider than the buns).

Toss broccoli on a baking sheet with a drizzle of olive oil and a pinch of salt and pepper. Roast in oven until lightly crisped, 15-20 minutes.

Heat a drizzle of olive oil in a large pan over medium-high heat. Add onion and cook, tossing, until soft, 5-6 minutes. Stir in 1 TBSP sherry vinegar (we sent more) and 1 tsp sugar. Simmer until liquid is nearly evaporated, 1-2 minutes. Season with salt and pepper. Transfer to a small bowl and set aside.

Line another baking sheet with parchment paper. Place cheddar on it in two even piles. Bake in oven until melted in middle and crispy at the edges, 5-7 minutes.

Meanwhile, heat a drizzle of olive oil in same pan over medium-high heat. Season patties all over with salt and pepper. Add to pan and cook to desired doneness, 3-6 minutes per side. Meanwhile, carefully remove frico from baking sheet. Discard parchment paper and place buns on sheet. Toast in oven until golden, 3-4 minutes.

Fill each bun with a burger, onion jam, tomato slices, ketchup, and a frico. Serve with broccoli on the side.