For broth, coat a roasting pan with vegetable oil and roast neck, back and wings of chicken with roughly cut vegetables in a 450 degree oven. Baste every 15 minutes with oil and turn until all is dark brown but not burned. Deglaze pan with a cup of water and turn all into a soup pot. Add 5 more cups of water and simmer one and a half hours. Strain, chill, remove fat and strain through cheesecloth.
For risotto, melt butter and oil in heavy-bottomed pan.
Saute onion until soft but not brown.
Add rice and cook until coated with fat.
Add wine and cook and stir until absorbed.
Add grated celery root and stir well.
Add 1 cup broth and stir every few minutes until absorbed.
Add chopped celery and mix.
Add second cup of heated broth. Now stir constantly, tasting frequently, just until the rice is cooked al dente and creamy. You may need all or part of the last 1/2 cup of broth, or use water.
Fold in the parmesan and season with drops of lemon juice, salt and pepper. Serve immediately with additional parmesan on the side.