Thanks to Zedupoca for the You Tube
I’m Gonna Sit Right Down and Write Myself a Letter was written in 1935 music by Fred E. Ahlert and lyrics by Joe Young. It was a big hit for Fats Waller in 1935. He recorded it on May 8, 1935. It later became a vocal standard with many of the top singers recording their versions. His Rhythm group on that date consisted of Herman Autrey, trumpet; Rudy Powell, reeds; Al Casey, guitar; Charles Turner, bass; Harry Dial, drums; and Fats, vocal and piano.
1935 was a very good year (as Chuck Cecil might say) for Fats Waller. His popularity soared and he was cranking a whole shelf full of these gems.