underplate
noun
Plural: underplates
A piece of material placed under something, such as protective or decorative mats arranged under dining plates, or metallic slabs inserted between the flames and pots when cooking to protect bottoms from uneven heating and fire-induced damage while effectively preventing focal food burning.
Examples:
With gas appliances, do not forget flame-shielding underplates / heat-output eveners or thick-bottomed utensils. (Source: J∙ Okram - Bartonian Potato Pancakes ● Cooking Recipe.)