These thick, soft, chewy chocolate chip cookies are best served warm, when the chips are still melted.
Position the oven racks in the top third and center of the oven and preheat the oven to 325 degrees. Line 2 large rimmed baking sheets with parchment paper or silicone baking mats.
In a medium bowl, whisk together the flour, baking soda, and salt. In a large bowl, beat the brown sugar, butter, sugar, and corn syurp with an electric mixer set on high speed until combined, about 1 minute. Beat in the egg, egg yolk, and vanilla. With the mixer on low speed, mix in the flour mixture, just until combined. Mix in the chocolate chips.
Using 2 tablespoons per cookie, drop the dough about 3 inches apart on to the prepared baking sheets. The mounts of dough can be frozen on the baking sheets until hard, then transferred to a zip-tight plastic bag and frozen for up to 1 month. Bake without thawing.
Bake, rotating the postiion of the sheets from top to bottom and from to back halfway through baking, until the cookies are lightly browned on the edges, about 18 minutes. (If frozen, bake for 20 minutes). Let cool on the baking sheets for 5 minutes. Transfer to a wire cooking rack and cool completley. Repeat with the remaining dough, on cool baking sheets.