Upaniṣads
Upaniṣads essentially means “to get closer”. “Closer” refers to that knowledge that releases all of us from the bondage of birth and death. These texts are a part of the Prasthāna Trayī or the epitome of Vedānta. The teachings in these are more reflective and contemplative than instructive. The goal is to contemplate and realise the Brahman. ~108 Upaniṣads are currently known. These convey the same idea in distinct ways so that individuals can choose the form that appeals to them the most. Acārya Śankara has identified 10 of these as the most important ones and written a commentary on them.
Prof. Mahadevan has covered Taittirīya and Muṇḍaka Upaniṣads in detail.