When melted, add the diced onion, the bay leaf, and the thyme sprigs. Cook until the onion is soft, without browning, about 12 minutes. Meanwhile, prepare the leek and celery root. When the onions are ...

If you like a little more texture to your toastie, it also works well with a tablespoon of finely diced celery folded through the filling. Tip the tuna into a bowl with the spring onion ...