225g/8oz caster sugar
200g/7oz icing sugar
225g/8oz self-raising flour
75g/2½oz walnuts
12 walnut halves, to decorate
225g/8oz unsalted butter, softened, plus extra for greasing
125g/4½oz unsalted butter
4 free-range eggs
50ml/1¾fl oz strong espresso coffee
50ml/2fl oz strong espresso coffee