a cooking pan with two parts, a bottom part for boiling water and a top part for holding food to be cooked by the steam from the water

Cook the sauce slowly over a low heat in a double boiler, stirring constantly. 在蒸锅中用小火慢煮酱汁，不断搅拌。

Melt the chocolate and butter gently together in the top part of a double boiler over simmering water. 将巧克力和黄油放在蒸锅上层，把水煮沸，使其慢慢融化。