Early French pain bescuit referred to bread baked twice. The phrase shortened before English borrowed it, and the spelling later changed.
Sources
- Merriam-Webster: biscuit
Kids Etymology and Word Origin explicitly explain the phrase, shortening and English spellings.
- Online Etymology Dictionary · biscuit
Meanings of the older forms on the word path.
- Cambridge Dictionary · biscuit
Meanings of the older forms on the word path.
- Centre National de Ressources Textuelles et Lexicales · biscuit
Meanings of the older forms on the word path.