A fancy word for a simple technique!
A bain-marie provides an even and gentle heat to cook delicate dishes such as custards, sauces, savoury mousses, and melting chocolate to avoid breaking or curdling them.
Add a couple inches of water to a pan and bring to boil on the hob.
Reduce to a simmer, place a heatproof bowl on top ensuring the bowl does not touch the water, then cook as per your recipe.
Stay focused when using a bain-marie to avoid scolding yourself.