Step 1

Put the chestnuts, almonds, prunes and milk in a small pan over a low heat, until the milk is almost, but not quite, boiling. Take off the heat and leave to sit for 10 minutes, then blend to a soft, rough paste.

Step 2

In a bowl over a pan of simmering water, melt the butter and chocolate, then leave to sit for five minutes. Heat the oven to 180C (160C fan)/gas 4.

Step 3

Add the chestnut paste to the chocolate mix. In another bowl, whisk the eggs, sugar and salt until soft and fluffy, then add to the mix and stir vigorously. Scrape into a 23cm-25cm tin lined with greaseproof paper, and bake in the middle of the oven for 25 minutes, until set but just a little wobbly at the centre.

Step 4

The cake will be soft and mousse-like inside, so leave to cool completely – at least an hour, but ideally three or overnight – before removing from the tin.