Heat the oven to 200°C/180°C fan/gas 6. Line a 20 x 7cm round cake tin (with removable base) with baking paper.

Grind 75g of the walnuts in a food processor until they resemble rough sandy crumbs. Then toast the remaining 75g of walnuts on a baking tray in the oven for 3–5 minutes, until they just give off a toasted smell and before they take too much colour – they should be just turning golden.

Rub them briskly in a clean tea towel to remove as much of the skins as you can. Pick out all the pieces of walnut, leaving behind the skins, and scrunch any whole nuts into smaller pieces.

Peel, quarter and core the apples. Slice each quarter lengthways, not quite all the way through to the tip. They should be just joined, but able to be spread out like a fan shape of very fine slices. Dribble with a little lemon juice to stop them browning while you make the batter.

Whisk the eggs and 200g of the sugar with the pinch of salt until the mixture becomes thick and forms trails.

Melt the butter in the milk over a medium heat until nearly boiling and add to the egg mixture, stirring all the time.

Fold in first the sieved flour and baking powder and then the ground walnuts, spoon by spoon. Try to work quickly and use as few cuts and folds as possible to keep all the lightness in the cake.

Pour the liquid batter into the prepared tin. Work fast (batter will be working already) to fan out the pieces of apple and push them down, core edge first, into the batter, arranging and spreading as much as you can.

Scatter the toasted walnuts over the surface. Sprinkle the remaining caster sugar over the top of the apple-studded batter.

Bake for 20–30 minutes, checking after 20 minutes for signs of done-ness. The cake should be light golden, all wobble gone, but still with a shadow of vulnerability.

Cool on a rack to just warm or leave to cool for eating later.