Gently melt the chocolate, butter and peanut butter, stirring until smooth and glossy. Remove from the heat, then stir in the broken biscuit, nuts, cherries, vanilla and salt until well combined.
Tip into a silicone cake tin (alternatively, you can line a brownie tin for a rectangular cake), pressing the mixture down with the back of a spoon. Place in the fridge to chill overnight, or until firm.
Now, make your topping (if using). In a Bain marie, gently heat your cream and dark chocolate, stirring constantly, until melted and glossy. Stir in the icing sugar. Pour over your cake, and allow to set in the fridge.
Serve at room temperature topped with fresh berries.
