Adjust oven racks to upper & lower -middle positions and heat oven to 325. Line cookie sheets with parchment paper. (Or if you have Silpat, this is the perfect time to use it).
Whisk dry ingredients together; set aside.
With electric mixer, or by hand, mix butter & 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 chips.
Roll 1 1/2 T dough into ball. Holding dough ball in fingertips of both hands, pull into 2 equal halves. Rotate halves 90 degrees and, with jagged surfaces facing up, place formed dough onto cookie sheet, leaving ample room between each ball. (This ensures that you'll have a bumpy, textured top, not the rounded tops where you can't see the chocolate chip goodness hiding below...)
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 & puffy (about 13-14 minutes in my oven).
Cool cookies on sheets until able to lift without breaking and place on wire rack to cool.
Makes about 30 cookies. I normally make 18 cookies when I make the dough (two cookie sheets with 9 cookies each) and freeze enough dough for another dozen cookies to bake another day. Here's how: