I make variations on beetroot gratin all the time, and this one with celeriac, dill and goat’s cheese is an absolute winner. You’ll want to use a mandoline (very carefully) for the celeriac, to make sure it’s sliced thinly enough to cook through in half an hour (alternatively, do everything in a food processor using the slicing/grating attachment). If you happen to have a bunch of salsify, or spot one when you’re out, by all means peel, slice and add that, too. This gratin tastes even better the next day, so it’s definitely worth having leftovers.
