Adjust oven racks to upper and lower-middle positions. Heat oven to 325 degrees.
Line cookie sheets with parchment paper.
Whisk dry ingredients together; set aside.
With electric mixer or by hand, mix butter and sugars until thoroughly combined.
Beat in egg, yolk and vanilla until combined.
Add dry ingredients & beat at low speed just until combined. Stir in chips.
Roll scant 1/2 c. dough into ball. Holding dough ball in fingertips of both hands, pull into two equal halves. Rotate halves 90 degrees and, with jagged surfaces facing up, place formed dough onto cookie sheet, leaving ample room between each ball. (I used a standard scoop instead.)
Bake, reversing position of cookie sheets halfway through, until cookies are light golden brown and outer edges start to harden yet centers are still soft and puffy, approximately 17 minutes.
Cool cookies on sheets until able to lift without breaking and place on wire rack to cool.