Step 1

Preheat the oven to 180°C/gas mark 4

Step 2

Begin by preparing the apple purée. Wash and dry the apples, then cut into quarters. Place on a baking tray and bake for 20–30 minutes, until soft

Step 3

Remove from the oven and leave to cool, reserving any liquid in the tray, then transfer the apples and their juices to a blender and blitz to form a smooth, sweet purée

Step 4

Preheat the oven to 170°C/gas mark 3.Line the bottom of an 18–20cm loose-bottomed cake tin with baking and grease the sides with a little oil

Step 5

Place the walnuts on a baking tray and toast in the oven for 5–8 minutes until beginning to colour. Leave to cool, then weigh out 80g and finely chop. Set the remaining walnuts aside

Step 6

Combine the milled flax seeds with the water and leave for 15 minutes to form a gel, stirring occasionally

Step 7

In a large bowl, mix together the finely chopped walnuts, ground almonds, chestnut flour, cinnamon, baking powder, bicarbonate of soda, salt and lemon zest. Make a well in the centre and add the flax gel, maple syrup, vanilla extract, oil and 60g of the apple purée. Mix well until combined

Step 8

Divide the mixture equally in two, placing half in the cake tin. Spread it out evenly with a palette knife to form a 1cm layer. Peel, core and thinly slice the apples and spread them over the cake mix, overlapping them in a circle

Step 9

Scatter the blackberries over the apple slices and top the fruit with the rest of the cake mix. The mix will be sticky so use your fingers to dab small bits of the mix over the blackberries (it doesn't matter if some berries are still showing, but try to cover most of them)

Step 10

Sprinkle the remaining walnuts over the top of the cake, breaking them roughly between your fingers as you do so. Press them into the cake mix slightly. Bake for around 30 minutes, rotating the tin halfway through baking

Step 11

If the top is looking a bit dark, turn down the oven to 160°C/gas mark 2.5 for the last 10–15 minutes. It is ready when the top is firm to touch and a rich golden brown, the nuts will be well toasted and a skewer inserted into the centre of the cake comes out almost clean

Step 12

Serve warm with an extra dusting of cinnamon or mesquite if you like and natural yoghurt. This is best eaten fresh but will keep for up to five days in a sealed container in the fridge