casserole vs double boiler

casserole

noun
  • Food that fills the high-walled dish or pan that it was cooked in. 

  • Food, such as a stew, cooked in such a dish. 

  • A dish of glass or earthenware, with a lid, in which food is baked and sometimes served. 

verb
  • To cook like, or as, a casserole; to stew. 

double boiler

noun
  • A large pan containing hot water, into which other smaller pans are set in order to cook food at low heat (below the boiling point) or to keep food warm. 

  • A pair of interlocking pots, the lower one filled with water which when boiling heats the contents of the upper pot. 

How often have the words casserole and double boiler occurred in a corpus of books? (source: Google Ngram Viewer )