Preheat the oven to 180 °C/350 °F/gas 4.

Grease a square baking tin (roughly 20 cm) with a little oil, then line with greaseproof paper.

Place a heatproof bowl over a pan of simmering water, making sure the base doesn’t touch the water. Break 150 g of chocolate into the bowl and allow it to melt, then set aside to cool slightly.

Meanwhile, sieve the flour and cocoa powder into a large bowl, then stir in the sugar and a pinch of salt. Halve the vanilla pod lengthways, scrape out the seeds, then add them tot he bowl. Stir in the oil, soya milk and melted chocolate until combined.

Roughly chop and stir in the remaining chocolate and most oft he walnuts, reserving a few for he top. Pour the mixture into the prepared tin, spreading it out evenly. Sprinkle over the remaining walnuts, then place into the hot oven for 20 to 25 minutes, or until cooked on the outside, but still gooey in the middle.

Leave to cool for around 5 minutes, turn out onto a wire cooling rack then serve warm.