Heat the oven to 200C/180C fan/gas 6. Line a 20cm square baking tin with baking parchment and set aside. Put the sweet potato halves in a different baking tin or tray and roast for 40-50 mins until softened. Leave to cool, then put in a food processor and blitz until smooth.

Reduce the oven to 180C/160C fan/gas 4. Tip the sweet potato mix into a bowl and combine with all the remaining ingredients, except the almonds and 50g of the dark chocolate. Spoon the batter into the prepared baking tray. Scatter over the almonds, if using, then bake in the oven for 30-40 mins until a skewer comes out with a few crumbs. Leave to cool. Melt the remaining dark chocolate in a heatproof bowl in the microwave for 30 seconds, stirring, then in 10-second blasts until melted. Drizzle over the brownies, then leave to cool before cutting into 12 or 16 pieces. Will keep in an airtight container for up to three days.