'baklavas' originates from Turkish, specifically the word 'baklava', where the root is thought to come from Ottoman Turkish 'baklawa' (and possibly influenced by nearby Persian/Arabic forms) with a sense related to a wrapped or layered confection.

'baklavas' changed from the Ottoman Turkish word 'baklawa' and the modern Turkish 'baklava', and was adopted into English as 'baklava' with the plural form 'baklavas' used for multiple pieces.

Initially it referred to the same layered sweet pastry in Ottoman/Turkish contexts, and over time the meaning has remained largely the same in English; only the form of the word adapted to English usage (including the plural).