Preheat the oven to 150°C and line an approx 23cm square tin with paper
Melt the chocolate in a microwave or a pan over water, stirring until melted and smooth
While the chocolate is melting, whisk the eggs and sugar together until the mixture is light and fluffy: this is easiest with an electric mixer with a whisk attachment
Stir the beaten eggs into the chocolate, then add the oil, spices, orange zest, cranberries and flour and gently mix until very smooth and glossy. Stir in the brandy if using. Pour into the prepared tin
Mix the honey/brown sugar into the chestnut puree. Drizzle the chestnut puree over the mix, then use a skewer or knife tip to gently swirl and marble the chestnut and chocolate mix it through. Sprinkle the chestnuts or nuts over the top
Bake for 20-25 minutes then remove and leave to cool in the tin, then chill in the fridge for about 1 hour at least
Cut into pieces with a sharp knife dipped into hot water and cleaned between each cut. Serve cold or at room temperature. It’s also remarkable straight from the freezer, with a coffee.