Peel and halve the shallots. Pluck the rosemary needles from the twig. Peel one pink and one yellow grapefruit thickly, removing the white skin completely. Remove the fillets with a knife between the skins, catching the juice.
Squeeze the rest of the grapefruit. Cook the pasta in boiling salted water for about 10 minutes. Rinse meat cold and dab dry. Cut into 8 medallions and beat slightly flat. Fry medallions in hot oil on both sides for about 3 minutes.
Season with salt and pepper. Remove from the pan and keep warm. Add the shallots and rosemary needles to the frying fat and fry for approx. 10 minutes, turning. Dust with flour and sauté. Add the grapefruit fillets and juice and bring to the boil once while stirring.
Season with sugar and pepper. Drain tagliatelle, rinse with cold water and drain well. Arrange hare medallions, grapefruit sauce and noodles on four plates.