Welsh onion cake with caerphilly

• butter↗200g g

  plus extra for the tin

• drizzle of oil
• large onions↗3

  thinly sliced

• leek↗1

  sliced

• floury potatoes↗1kg kg

  such as Maris Piper or Désirée, peeled and thinly sliced (use a mandoline or the fine slicing blade of a food processor)

• Caerphilly↗150g g

  cheese, crumbled (or another sharp, crumbly cheese)

Step-by-step instructions

1. 1

   In a large pan, heat a knob of the butter with a drizzle of oil. Once the butter is foaming, add the onions, leek and some seasoning and cook for 15 mins until the onions are soft and sticky, stirring occasionally. Butter a 22cm cake tin or baking dish (alternatively, you can assemble the cake in the pan you’re already using if it’s ovenproof).

2. 2

   In a separate pan, melt the remaining butter. Toss the sliced potatoes with the melted butter and plenty of seasoning. Heat oven to 200C/180C fan/gas 6.

3. 3

   Arrange the potato slices over the base of the dish in a spiral or in concentric circles. Top with some of the onion mix, sprinkle over a layer of cheese and continue layering, finishing with a final round of potato slices. Press down firmly with your hands to compact the layers. Bake for 45-50 mins until the potatoes are golden brown and tender; cover with foil if the cake starts to take on too much colour. Turn out onto a plate to serve.