Up the hill 30 metres from and equidistant from the Aretes Boulder and the Purple Slab, at the apex of the triangle, so to speak. If you know what a howff is, you can't miss the boulder!
Span from the big starting hold to a good (but dubious) flake below the lip. Pull over straight from this (6c+) using advanced mantling technique or brute force. Alternatively, traverse the lip rightwards and pull over at leisure (6b). Avoid the big block for your feet (easy to do).