Abbot and Doctor of the Church; the Mass is In medio Ecclesiae aperuit os eius.
Father Grodziski is in fact using the formulary In medio Ecclesiae this morning (although I'm watching the recorded video and the not the live-stream which I guess happened at midnight, tsk).
The Offertory antiphon is Justus ut palma florebit.
And the antiphona ad Communionem is Fidélis servus et prudens.
For some reason I have a headache which is repressing my ordinary prolixity.