Soak the raisins in the rum for 3 hours, or preferably overnight.
Preheat the oven to 170C/150C Fan/Gas 3½. Grease and line a 20cm/8in square brownie tin with baking paper.
Melt the chocolate and butter together in a heatproof bowl placed over simmering water, ensuring the bowl doesn't touch the water. Stir to combine and set aside to cool slightly.
Blend the peas to a purée in a food processor. Add the eggs, sugar and cocoa powder and blend until smooth. Pour in the chocolate mixture and blend until smooth. Add the raisins and their soaking liquor and pulse until combined
Pour into the prepared brownie tin, bake for 20–25 minutes until set, but still a bit squidgy. Allow to cool completely in the tin before cutting.
Carlin peas have many names – black badger, grey or maple peas. You can use dried peas if you like, just soak them overnight and boil them for 1 hour until tender before using as per the recipe. You can also substitute black beans if you can't find carlin peas.