Method
Melt the butter, syrup and chocolate powder in a pan over medium heat. Add the raisin and mix together with a wooden spoon. Crush the digestive biscuits in a bowl with a rolling pin. Add to the chocolate and stir until the biscuits are well coated. Tip into a 18cm (7inch) square tin and spread out evenly.
For the topping:
Melt the butter with the chocolate in a bowl over a pan of simmering water and mix until smooth and glossy. Spread over the biscuit base. Leave to set in the fridge before cutting into squares.
The topping can also be made in the microwave. Melt the butter, add the chocolate and stir. Return to the microwave for ~ 10 seconds then mix until smooth and glossy.
A square of this with a cup of coffee satisfies that “must have a bit of chocolate” desire.