Belgian Beer Burger with Onion Pan Sauce

• 1 medium Yellow onion
• 1 tbsp Rapeseed oil
• 300 g Minced beef
• 1 tsp Fine sea salt
• ½ tsp Black pepper
• 200 ml Ale beer
• 60 g Emmental cheese
• 2 pieces Brioche bun
• 2 tsp Dijon mustard
• 4 leaves Butterhead lettuce

1. Halve and thinly slice the onion. Separate the lettuce leaves and set aside. Slice the brioche buns in half if needed.
2. Heat the rapeseed oil in a large frying pan over medium heat. Add the onion with a pinch of the salt and cook for 8 to 10 minutes, stirring, until soft and lightly golden. Tip the onion onto a plate, leaving any fat in the pan.
3. Put the minced beef in a bowl and season with the remaining salt and the black pepper. Shape into 2 patties, pressing a slight dip in the centre of each so they cook evenly. Keep them chilled while the pan heats if your kitchen is warm.
4. Return the pan to medium-high heat and add the patties. Cook for 3 to 4 minutes per side until well browned and cooked to your liking. Transfer to a plate to rest while you make the sauce.
5. Lower the heat to medium and add the cooked onion back to the pan. Pour in the ale beer and simmer for 4 to 6 minutes, scraping up any browned bits, until reduced to a glossy, spoon-coating sauce. Taste and adjust with a little more black pepper if you like.
6. Nestle the patties back into the pan and spoon the beer-onion sauce over them. Top each patty with the emmental cheese, cover the pan with a lid, and cook for 1 to 2 minutes until the cheese melts. Keep the heat gentle so the sauce does not reduce too far.
7. Toast the brioche buns cut-side down in the pan for 30 to 60 seconds until golden, working in batches if needed. Spread the Dijon mustard over the bun bases. Add the lettuce, then the cheesy patties, and spoon over any remaining beer-onion sauce before closing the buns.

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