Pesachim 75 - Instructions on cooking and eating the Passover lamb

Since the Passover offering must be "roasted over fire," one must be careful when cooking. If they notice that the meat has touched the earthenware part of the oven while cooking, they need to scrape this part off. In this place, it was roasted due to the oven wall's heat, not open fire.

If some gravy dripped onto the earthenware and then splatted back onto the meat, they should remove the meat in that place, to the depth of one finger - again, since in that place, it was boiled. 

After cooking, they can smear the dry meat with liquids. If they smeared it with oil, and that oil was "terumah" (the special gift that is given to the Kohanim priest that only they are allowed to eat) - here is what they do. If the people at the Seder are all Kohanim, they can eat the meat. But if some are regular Jews, they need to clean it. If the meat in this place was raw and did not absorb the oil, they simply rinse it. However, if it was fried and absorbent, they will need to remove the meat in that place, to the depth of one finger.

Art: Still Life with Earthenware by Vincent van Gogh