This route follows the slim leftmost dihedral on the southeast face of Yak - the first dihedral left of the Porcelain Chicken dihedral. Gain the dihedral from the right as per Porcelain Chicken or from below by soloing up the endless opening slabs as per Madness. Climb four to five long pitches up the dihedral (5.7 through 5.9, some granular rock, gear to 4"). Climb a shorter pitch up the dihedral as it pinches out, to gain a slabby ledge between two large roofs - one below and one above.
Squeezed up in an undignified manner on this shelf between the two roofs, traverse the hanging slab leftwards (the crux, 10a with sparse pro). This eventually leads into Yak Crack's upper dihedral, although it is possible to continue hard left to gain the 5.11a fingercrack variation to Yak Check pioneered by Croft and Foweraker.
From the base of Yak below the Yak Crack start, follow the base of the slab up and right until the objective dihedral is visible and have at'er.
Walking off from the top is best.
Full rack to 4". Some belays may be bolted.