Adjust oven racks to upper and lower-middle positions. Preheat oven 325°. Line two cookie sheets with parchment paper.
Whisk dry ingredients together in a medium bowl; 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 and beat at low-speed just until combined. Stir in chocolate chips.
Roll a scant half-cup of dough into a ball. Holding dough ball in fingertips of both hands, pull apart 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. Bake, reversing position of cookie sheets halfway through baking, until cookies are light golden brown and outer edges start to harden yet centers are still soft and puffy (approximately 11-14 minutes). Do not overbake.
Cool cookies on sheets until able to lift without breaking. Transfer to a wire rack to cool.