Preheat the oven to 180oC. Grease and base line a 21cm cake tin.
Place the dates and bicarbonate of soda in a bowl with 150ml boiling water and leave for 10 minutes. Blitz with a stick blender until smooth.
Meanwhile, whisk the butter and sugar together until pale and fluffy, whisk in the eggs, 1 at a time. Stir in the date mixture followed by the flour and then the walnuts. Spoon into the prepared tin and bake for 50-55 minutes until a skewer comes out clean. Allow to cool slightly before removing from then tin.
Place all the toffee and walnut sauce ingredients in a small saucepan and cook until bubbling and the butter has melted, allow to cool before spooning over the cake, allowing some to drizzle down the sides.
Cooks tip: This will keep for 2-3 days, great served warm with ice cream.
