Blend together 3 tablespoons flour, lemon juice and 1 quart water. add celeriac, set aside. Brown lamb in butter for 6 minutes. add onion, saute 5 minutes. add stock, boil, cover, simmer 50 minutes. Transfer celeriac to lamb mixture. add dill, salt and pepper, cover simmer 20 minutes. blend remaining flour with 3 tablespoons water, add to lamb, boil, simmer 1 minute. blend egg with cornstarch, pour mixture into saucepan, stirring constantly, cook until mixture thickens, about 2 minutes, do not boil. Serve with rice pilaf.