Exodus 12:9-10

12:9 Do not eat it raw ¹  or boiled in water, but roast it over the fire with its head, its legs, and its entrails. 12:10 You must leave nothing until morning, but you must burn with fire whatever remains of it until morning.

[12:9]  ¹ sn This ruling was to prevent their eating it just softened by the fire or partially roasted as differing customs might prescribe or allow.