Shalom. If I place a Stam Keli (e.g., a metal pan) (with no food in it) on top of a Blech or Hotplate on Erev Shabbos and on Shabbos Morning remove the Keli to a counter and then place a semi solid, semi liquid item on top of the hot Keli (while on the counter) to warm it up, is this permissible? Is this LeChatchila? Thank you.
In your theoretical case, it will depend if the food is considered a solid or liquid. If it is a liquid or if it contains liquid, then if the pan will be able to make the liquid reach yad soledes bo it s not permitted. If however the food is a solid then it would be permitted.