i know that i've seen what you are looking for but cannot find it.
these two links show the technique you are looking for. but they don't have the 1/4" seam sewn first... they just clip within the 1/4". i wasn't getting any results until i entered the term 'inside corners' to the search.
https://ankastreasures.wordpress.com...e-your-skills/
http://www.fonsandporter.com/article..._quilt_corners
HTH