Beat the butter and sugar smooth. Add the lightly whisked eggs and grated fruit peel. Rinse currents in hot water and dry them. Add them and the flour, baking powder and liquid.
Place the dough – which is quite thick – in a well-oiled ring mould, approximately 1 1/2 litres.
Bake on a rack on the bottom shelf at 300 F / 150 C barely 1 1/2 hours. The cake should be a week old before being sliced.