1 large onion
a teaspoon of thyme leaves
100ml vegetable stock
Peel the onion and slice it into thin rounds. Put them in a large mixing bowl. Peel the parsnips and celeriac and cut them into very thin slices. Toss them with the onion.
Set the oven to 190C/Gas 5. Melt the butter in a shallow ovenproof pan, then add the vegetables, layering them neatly or just chucking them in as the mood takes you, seasoning with the thyme leaves, pepper and salt as you go. Now pour the stock over the top.
Cover with a circle of greaseproof paper or kitchen foil, pressing it down well on the top of the cake. Bake for about an hour and ten minutes, until tender to the point of a knife. Remove the cover, turn up the heat to 220C/GAs 7 and bake for a further ten minutes, until the top has coloured and crisped a little.