Spicy beef and lentil burgers

Method

1. Place half the lentils and all of the stock in a medium saucepan and bring to the boil. Boil for 15 minutes, then reduce the heat to a simmer and continue to cook uncovered for 30 minutes, or until all the stock has been absorbed by the lentils. Keep an eye on the lentils towards the end to make sure they don’t catch on the bottom of the pan. Fluff the lentils up with a fork and leave to cool.
2. Put the remaining lentils in a food processor and blend to a powder.
3. Heat the oil in a frying pan over medium heat. Add the onion and fry for 2–3 minutes, until starting to soften. Add the garlic and fry for another 3 minutes, or until the onion is just starting to colour. Leave to cool.
4. Combine the minced beef, cooked lentils, lentil powder, fried onion, egg, lemon zest and harissa in a large bowl. Season with salt and pepper and mix well. Form into 10 cm burgers. Refrigerate until needed.
5. To make caramelised onions for the burgers, put the red onion in a heavy-based saucepan with 3 tablespoons of water. Bring to the boil. Cover with a lid, reduce the heat to a simmer and cook for 10–12 minutes until very tender and starting to caramelise.
6. Heat a non-stick frying pan or barbecue grill over high heat and cook the burgers for 3–4 minutes on each side, or until cooked to your liking.
7. Serve the burgers in lettuce leaves topped with the caramelised onions, tomato sauce and mayonnaise.