Sentence examples for once in from inspiring English sources

"once in" is a correct and common phrase in written English.
It is usually used to indicate a specific time or frequency in the past. For example: - "Once in a while, I like to treat myself to a fancy dinner." - "She told me that she had been to Paris twice, but only once in the winter." - "Once in a blue moon, I'll go for a run in the early morning." - "I used to ride my bike to work, but now I only do it once in a blue moon." In these examples, "once in" is used to specify a specific time or frequency in the past, such as "once in a while," "once in the winter," "once in a blue moon." It can also be used to indicate a one-time occurrence, such as "I saw a shooting star once in my life."