1Adjust oven racks to upper and lower-middle positions. Heat oven to 325 degrees.
2Line cookie sheets with parchment paper.
3Whisk dry ingredients together; set aside.
4With electric mixer or by hand, mix butter and sugars until thoroughly combined.
5Beat in egg, yolk and vanilla until combined.
6Add dry ingredients & beat at low speed just until combined. Stir in chips.
7Roll 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.)
8Bake, 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.
9Cool cookies on sheets until able to lift without breaking and place on wire rack to cool.