This creamy gratin is a special treat for fennelphiles. The nuttiness of the Gruyère partners beautifully with that gentle aniseed flavour. Frankly, I could lap up the fennel-vermouth-and-cheese-deepened cream with a spoon. And often do. While it’s rich and deep in flavour, it is fairly fluid; if you want it to be thicker, make the gratin up ahead of time, since it thickens as it stands.
I often halve this for two, baking it in a shallow round ovenproof dish 23cm in diameter and 5cm