Soak the dates. Pour the boiling water and espresso over the chopped dates. Stir in the bicarbonate of soda and leave for 10 minutes. Mash lightly with a fork.
Make the sponge. Cream the butter and sugar until light and fluffy. Beat in the eggs one at a time, then mix in the black treacle. Fold in the flour and baking powder, followed by the date mixture.
Bake. Pour the mixture into a lined 23cm square baking tin. Bake at 180°C (160°C fan) for 30 to 35 minutes, or until a skewer inserted into the centre comes out clean.
Make the sauce. Add the butter, muscovado sugar and double cream to a saucepan. Heat gently, stirring until smooth. Simmer for 2 to 3 minutes, then stir in the espresso and sea salt.
Serve. Pour some of the warm coffee toffee sauce over the sponge while it’s still warm, allowing it to soak in. Cut into squares and serve with plenty of extra sauce.
