Creamy chicken and butternut squash gratin

Method

1. 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 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.
2. Melt the butter in the pan, stir in the flour to make a roux (paste) and cook for 2-3 minutes. Add the stock, a little at a time, to the roux, stirring until smooth. Add the mustard, thyme and crème fraîche. Season and stir in the  chicken and the reserved onion, leek, squash.

3. 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.