Heat oil in a saucepot and add onion and celery. Sauté over medium heat until tender, about 5 minutes.
Add acini di pepe pasta and stir to coat. Add wine and stir until absorbed (a wooden spoon is best).
Soak saffron in warmwater for a minute, then add to pot with lemon zest. Stir in chicken stock, half a cup at a time, stirring until liquid is absorbed before next addition.
Stir in butter, season to taste and garnish with grated Parmesan and chopped parsley. Serve immediately.
Alternately, (to prepare ahead of time), acini di pepe can be cooked until half the liquid has been added, then spread on a baking tray to cool.
Chill until ready to serve, then slowly reheat with remaining stock. Finish as above.