The Taittiriya Upanishad is a Sanskrit text. It is one of the older, "primary" Upanishads commented upon by Shankara. It is associated with the Taittiriya school of the Yajurveda.
Ch 4: Mandukya Upanishad by Swamini Atmaprakashananda
Taittiriya Upanishad by Vidyasankar S
Mundakopanishad by Swamini Svatmavidyananda
Mundakopanishat by MLN Murthy
Taittiriya Upanishad by Babaji Bob Kindler