Sauté leek and celery in oil in a large saucepot over medium heat until tender, about 5 minutes.  Rinse barley until water runs clear and drain well.  Add barley to pot and sauté for 3 minutes.  Flood barley with wine and stir until liquid is incorporated.  Add stock, 1 cup (240 mL) at a time, stirring frequently, until all liquid is absorbed.  Before adding final portion of liquid, add rosemary and orange zest and juice.  Season to taste.  Immediately before serving, stir in butter and cheese until melted. 

NOTE: The rosemary may be sustituted for thyme if you would like a different flavour in the risotto. Other variations include using less rosemary as it may overpower the other ingredients.