Heat the oven to 180C/160C fan/gas 4. Butter the base and sides of a small baking dish. To make the sauce, sieve the cocoa powder into a jug and stir in the caster sugar. Gradually pour in 250ml boiling water until well combined and smooth. Set aside.

For the cake, sieve the flour and cocoa powder into a large bowl and stir in the sugar and espresso powder. Make a well in the middle and pour in the melted plant butter, Jord oat drink, and vanilla, whisking until smooth. Stir through the chopped chocolate and spoon into the prepared baking dish. Carefully pour the hot sauce into one of the corners, pouring it over the back of a spoon so it does not make a hole. Bake for 40-45 mins until a skewer inserted gently into the middle comes out with a few crumbs clinging to it (make sure you are just testing the pudding, not going all the way down to the sauce). Leave to stand for a few minutes before serving.