If you have a food processor, pour dry ingredients into a
food processor, and add in the cold cubed butter and pulse a few times until ingredients start to clump together. Pulse in the vanilla, yogurt, egg yolk and chocolate chips until just combined. Do NOT over mix. Dough will be VERY sticky and doesn't hold together very well. If you do not have a food processor, you can mix the ingredients by hand using a
pastry blender.