Don't miss out on our special Christmas issue with free 2023 calendar - subscribe by 18 October!
Preheat the oven to 220C/gas 7/fan 200C. Boil up a big saucepan of water.
Meanwhile trim the roots off each fennel bulb, remove the first leaf, then keep trimming off more root and removing more leaves, right down to the core. Cut off and discard (or keep for a stock) all the green stalky bits and coarse outer leaves. Slicing along the grain of the leaves, cut them into tulip-petal sized pieces.
Throw the fennel into the boiling water, cover the pan and bring back to the boil. Remove the lid and boil for 5 minutes to blanch the fennel, then drain thoroughly.
Lightly butter a large (about 25cm diameter) gratin or other ovenproof dish. Spread half the fennel over the bottom of the dish and strew evenly with half the olives. Cover with the remaining fennel and olives and season well. Pour over the cream, then sprinkle a thick layer of cheese on top.
Bake the gratin on the middle shelf of the oven for about 20 minutes or until the cream is bubbling, the top lightly gilded, and the fennel tender. Leave to cool for 5 minutes before serving.