Preheat the oven to 200ºC

Place the grated celeriac into a clean tea-towel and squeeze very hard to remove as much moisture as possible.  Tip it into a large bowl, and add the lemon zest and juice, a generous seasoning of salt and pepper, and the beaten egg.  Mix thoroughly with a fork until fully combined.

Grease a baking tray with a little of the butter, then shape the mixture roughly into 6 'cakes' and place them on the tray.  Brush each cake liberally with melted butter and bake for 10 minutes until golden brown on top.

Remove from the oven, then flip each rösti over.  The best way to do this is with a large fish slice or spatula, and being as fast and firm as possible.  Don't worry if they fall apart a bit - (which they will, I promise) - you can just squash them back together again.  Return them to the oven for a further 10 minutes or until golden and crispy on top.

I served mine topped with a little stilton (popped on top for the last minute of cooking) and a poached egg, with shitake mushrooms and cherry tomatoes on the side.  But these would also make a hearty breakfast with brown sauce, or a side-dish to a Yorkshire Pudding Sunday Lunch.