Rack of lamb on Welsh onion cake

Method

1. Preheat the oven to 200C/gas 6.

2. Peel the potatoes and slice very finely with a mandolin or sharp knife. Toss with the melted butter and season with plenty of salt and black pepper.

3. Brush a shallow ovenproof dish with a little a little more melted butter. Layer the potato and onion in the dish, starting with potato and finishing with a neat layer of overlapping potato slices. Drizzle any remaining butter over the top.

4. Cover the dish with foil and bake in the oven for 1 hour. Meanwhile, take the lamb out of the fridge to come to room temperature.

5. After the onion cake has had an hour in the oven, remove the tin foil. Sit the lamb racks on top with their bones interlaced and tuck the rosemary sprig in the middle. Return to the oven for 15-25 minutes, depending on the size of the racks and how you like your lamb cooked. By now the potatoes should be beautifully tender and browned on the top.