1.Combine currants and vinegar in a small bowl; stand for 15 minutes.
2.Meanwhile, coarsely chop reserved radish leaves.
3.Cook pasta in a large saucepan of boiling salted water until almost tender. Drain, reserving 1 cup cooking liquid.
4.Meanwhile, heat oil in a large frying pan over high heat; cook radishes, stirring occasionally, for 3 minutes or until browned. Add currant mixture, radish leaves, garlic, pine nuts and sage; cook, stirring, for 1 minute or until fragrant and leaves are wilted. Season.
5.Add pasta to the frying pan with half the cheese, the remaining oil and enough of the reserved cooking liquid to coat; season to taste. Serve topped with remaining cheese.
Use the freshest, best radishes you can buy. The radishes should be firm, and the leaves crisp and bright green. We used 16 radishes and about 2½ cups of radish leaves in this recipe.