Quarter the fennel lengthways, and cut out and discard the root.

Thinly slice the fennel.

Heat 2 tbsp of the oil in a large frying pan, season the fennel and gently cook for about 5 mins until starting to soften.

2)Drizzle a little oil over the base of a 1.5-litre gratin dish.

Arrange half the potatoes over the base, then season.

Spread the fennel over, then cover with the remaining potatoes.

Pour over the stock, season and drizzle with the remaining oil.

Scrunch a piece of baking parchment around the edge of the dish to make a seal, then bake for 1 hr.

Can be made a few hours ahead up to this point.

3)Remove the dish from the oven and put the tomatoes on top.

Scatter over the Parmesan and return to the oven for 20 mins until the top is golden.