The correct spelling of "tost it in" is actually "toast it in". The word "toast" is pronounced /təʊst/ in IPA phonetic transcription. It is spelled with a "o" followed by an "a" as it comes from the French word "toster". The added "t" in "toast" compared to "tost" is because it is a past tense form of the verb "to toast". The phrase "toast it in" is commonly used in cooking and refers to the act of placing something, such as bread or cheese, in a toaster or under a grill to be heated or browned.