Pod the broad beans. Peel the shallots and cut into quarters. Peel and thinly slice the garlic. Zest the lemon. Finely shred the sorrel.
Crumble half the stock cube into a jug. Pour over 200ml hot water from the kettle. Swirl to dissolve.
Heat a lidded frying pan. Add 2 tsp oil. When hot, season the chicken thighs and add them to the pan. Cook for about 15 mins till golden brown, turning 2-3 times.
Drain the pan of any excess fat. Add the shallots to the chicken. Cook for 2 mins. Add the garlic. Cook for 1 min. Add the stock. Cover and simmer gently for 5 mins.
Add the buckwheat to the pan and shuffle about so it is evenly distributed. Cover. Simmer for 10-15 mins till the buckwheat is tender and the chicken is cooked through. Stir the buckwheat occasionally to make sure it cooks evenly.
Turn the heat off under the chicken and leave to rest for a few mins. Cut the baby gem into 8 wedges. Melt the butter in a small frying pan till foaming. Add the lettuce and cook for 2 mins, turning once. Add the broad beans. Cook for 1 min more.
Stir the lemon zest into the broad beans and lettuce and tip the whole lot over the chicken and buckwheat. Serve up, garnished with the shredded sorrel and a wedge of lemon.