This is a traditional Cornish recipe. Saffron colours the cake bright yellow, and gives it its distinctive flavour. Saffron comes from the autumn-flowering crocus sativus and is expensive to buy - the saffron is the stigmata of the crocus, and over 4000 blooms are required to give one ounce of saffron.
Rub the butter in the flour, add the salt, sugar, finely chopped peel and the currants. Warm a little milk and pour it over the yeast and one teaspoonful of sugar in a basin. When the yeast rises, pour it into a well in the centre of the flour. Cover it with a sprinkling of the flour, and when the yeast rises through this and breaks it, mix by hand into a dough, adding milk as needed, as well as the saffron water. Leave in a warm place to rise for a while.
Bake in a cake tin for about 1 hour at 350F.