Step 1

Preheat the oven to 220C/200C Fan/Gas Tip the leeks, fennel and squash into a roasting tin large enough to hold everything in roughly one layer, then stir through the olive oil, salt, chilli and half the tarragon. Roast for 45 minutes, or until the squash is just cooked through.

Step 2

Meanwhile, finely chop the remaining tarragon leaves.

Step 3

Pour the cream or crème fraîche over the vegetables, then scatter with the chopped tarragon, hazelnuts and cheddar. Turn the oven down to 200C/180C Fan/Gas 6 and return the gratin to the oven for a further 15 minutes.

Step 4

Leave the gratin to cool for 10 minutes before serving, with crisp rounds of toasted bread.