- For the chicken
- 1 x 1.6kg (3½lb) roasting chicken
- ½ onion
- 2 celery stalks, roughly chopped
- 1 carrot, roughly chopped
- 2 bay leaves
- 10 black peppercorns
- 4 sprigs fresh thyme, rolled up in a strip of leek
- For the sauce
- 50g (2oz) butter
- 2 leeks, sliced on the diagonal
- 25g (1oz) plain flour
- 75ml (3fl oz) white wine
- 1tbsp wholegrain mustard
- 2tsp Dijon mustard
- 300ml (½pt) crème fraîche
- 125g (4½oz) Gruyère cheese, ½ cubed and ½ grated
- For the topping
- 65g (2½oz) fresh breadcrumbs
- 1tbsp lemon thyme, leaves only
Put the chicken ingredients into a deep pan and pour over enough cold water to cover the bird fully. Cover with a lid and bring to the boil. Simmer for 1 hour 15 minutes or until the meat is cooked. Remove the chicken from the poaching liquid and cool slightly.
Shred the meat, pulled from the carcass, then make a stock: return the bones to the pan and boil until reduced to about 500ml (18fl oz).
To make the sauce, melt half the butter and fry the leeks until tender. Remove from the pan and set aside. Preheat oven to 180 C, 160 C fan, 350 F, gas 4. Melt the remaining butter in the pan and stir in the flour to make a roux. Cook for 1 to 2 minutes. Gradually pour in the strained stock, stirring all the time until the sauce thickens. Add the wine and bubble for a further minute. Finally, stir in all the mustard and the crème fraîche until combined. Season to taste. Remove from the heat.
Arrange the chicken, leeks and cubed cheese in a 1 litre (1¾pt) ovenproof baking dish. Pour over the sauce. In a bowl, combine the breadcrumbs, grated cheese, thyme leaves and black pepper to taste.
Sprinkle over the chicken and bake for 45 minutes or until the topping is golden and the sauce is bubbling around the edges.
Top Tip for making Creamy Chicken Gratin with Crunchy Lemon Thyme Topping
After step 4, freeze the crumbs and chicken filling separately. Thaw the filling in the fridge overnight, then top with the thawed crumbs and bake as per step 5.