01
The rule
SA (OC 318:4) rules: a fully cooked dry item may be reheated even in a first vessel - no cooking. With a cooled liquid the SA is strict, and the Rema notes leniency when not fully cooled.
Kushya
Question: is reheating dry food on a plate "returning"? Answer: two separate questions: cooking (none for dry) and "appearing to cook" (depends on the method).