Soak the rabbit joints in salted water for two hours and dry well. Mix together the flour and suet with a pinch of salt and enough cold water to make a firm dough. Roll out the dough and use two-thirds to line a pudding basin. Slice the onion and chop the sage, mushrooms and bacon. Arrange alternate layers of rabbit, onions, sage, mushrooms and bacon in the basin, adding a sprinkle of flour, salt and pepper to the layers. Cover with water and put on the remaining suet dough as a lid. Put on a piece of greaseproof paper and foil or a pudding cloth, and steam for three hours.