In a large mixing bowl, whisk together the flour, baking soda, cornstarch, and salt. Set aside this dry mixture.

In another bowl, blend the melted butter with both sugars until smooth. Beat in the egg and yolk, then incorporate the vanilla extract, resulting in a thin and shiny mix.

Combine the wet ingredients into the dry mix, folding gently until just incorporated. The resulting dough should be shiny, soft, and somewhat thick. Add the chocolate chips and carefully mix them in.

Wrap the dough securely in plastic wrap and place it in the refrigerator for at least 2 hours, or up to 3 days. Overnight chilling is recommended for optimal results.

Preheat the oven to 325°F (163°C) and prepare baking sheets with parchment or silicone liners. If dough has been chilled longer than 2 hours, allow it to sit at room temperature for 15 minutes before shaping.

Scoop out portions of dough weighing roughly 2 ounces for large cookies or about 1.75 ounces for medium ones. Form them into balls and slightly elongate them to maintain thickness while baking, spacing them 3 inches apart on the trays.

Bake for 13 to 14 minutes, until the edges turn a light golden brown while the centers remain soft. Allow cookies to cool on the baking sheet for about 10 minutes before transferring them to a wire rack to cool completely. Optionally, press a few extra chocolate chips on top of the warm cookies for added appeal.

Store cooled cookies in an airtight container at room temperature for up to one week, if they manage to last that long!