1.5kg large free-range chicken (see method)
2 large onions, roughly chopped
2 leeks, thickly chopped
1 carrot, chopped
2 bay leaves
5 black peppercorns
Small bunch fresh thyme, chopped, plus a few leaves for sprinkling
3 tbsp olive oil
350g butternut squash, peeled, deseeded, chopped into 2.5cm pieces
75g plain flour
1 tsp Dijon mustard
3 tbsp crème fraîche
75g ciabatta, torn into rough pieces
60g Gruyère, grated
1. Place the whole chicken in a large saucepan with 1 onion, 1 leek, the carrot, bay leaves, peppercorns and half the thyme. Cover with cold water and bring to a boil. Gently simmer for 45 minutes until cooked through.
2. Remove the chicken and set aside until cool enough to handle. Remove all the meat from the carcass, shred into bite-size pieces, then divide in into 2 piles (you should have about 700g meat in total. You only need 350g for this recipe; save the rest for the Chicken enchiladas recipe) and set aside. Return the bones to the pan of stock. Put over a medium-low heat and simmer for 1-2 hours, or longer if possible. Strain into a jug, discarding the solids, then season and set aside.
3. Preheat the oven to 200°C/fan 180°C/gas 6. Heat 1 tbsp oil in a large pan over a medium heat. Add the remaining onion and leek and fry until soft. Remove from the pan and set aside. Add the squash, season and fry for 10 minutes until tender. Set aside with the onion and leek.
4. Melt the butter in the pan, stir in the flour to make a roux (paste) and cook for 2-3 minutes. Scoop any fat off the surface of the stock. Measure 800ml (freeze the rest). Add it, a little at a time, to the roux, stirring until smooth. Add the mustard, remaining thyme and crème fraîche. Season and stir in the veg and chicken.
5. Spoon evenly into a 2-litre ovenproof dish. Scatter with the ciabatta pieces, Gruyère and extra thyme. Season, then drizzle with the rest of the oil. Bake for 20 minutes until golden and bubbling hot. Serve the gratin with peas.
- To freeze: make the gratin, but don’t cook it. Wrap in cling film, then foil, and freeze for up to 3 months. Defrost and cook as described.