Preheat oven to 350° F. Line two baking sheets with parchment paper or a Silpat mat. Set aside.
In a medium bowl, whisk to combine flour, cornstarch, baking soda, and salt. Set aside.
Cream butter and sugars in the bowl of a stand mixer fitted with a paddle attachment, until lightly colored and fluffy. Add egg and vanilla, and mix to combine.
Slowly add dry ingredients and mix on low speed until combined. Do not over mix. Stir in chocolate chunks with a sturdy spatula.
Using a tablespoon size scoop, drop dough onto prepared baking sheets. Bake for 8-10 minutes, until barely golden brown around the edges. (The tops will not brown, but do NOT cook longer than ten minutes.)
Let cookies cool on the baking sheet for 3 minutes, then transfer to a wire rack to cool completely.
Notes
Recipe slightly adapted from Anna Olson, Food Network Canada