Sweat onions in 1/2 lb of butter until soft, season with salt and pepper. Drain Farro and to onions. Toast Farro five minutes. Add white wine. Cook Farro until wine is reduced to almost dry, stirring continuously. Add hot water, 2-3 cups at a time. Each time stirring and cooking Farro until reduced to almost dry. Finish with the last pound of butter and the Parmesan. Adjust salt and pepper.