That sounds like a **defrosting tray**, also called a **thawing plate**. The older product you remember may have been **Miracle Thaw**: a black aluminium slab with grooves, advertised using exactly that ice-cube demonstration. [This 1997 *ChemMatters* article describes it](https://teachchemistry.org/pdf/2020/08/27/15/17/29/f474b1a2-6120-4cef-82c7-b69259b5cdd1/OCT97.PDF).

The trick is **heat conduction**. Aluminium transfers heat readily. It feels cold because it quickly draws heat from your warmer hand, but it is still warmer than ice—so it transfers heat into the ice and melts it. No electricity is needed.

To find one, search for **“aluminium defrosting tray”**, **“meat thawing plate”**, or **“Miracle Thaw.”**