Preheat oven to 350 degrees F. Line baking sheets with parchment paper and set aside.
Using a stand mixer fitted with the paddle attachment (or a large mixing bowl with a hand mixer), combine the butter, vegetable oil, granulated and brown sugars, eggs and vanilla and beat on medium speed until creamy and free of lumps.
In a separate bowl, combine the flour, baking powder, baking soda, corn starch and salt. Mix well. Gradually add to the butter mixture and beat on medium speed until just combined.
Fold in the chocolate chips. Cover the bowl and refrigerate the dough for at least 30 minutes, or until it is firm enough to scoop.
Scoop 1 1/2-tablespoon portions of chilled dough onto the prepared baking sheets, spacing them 2 inches apart. Gently flatten each mound of dough. If desired, press a few reserved chocolate chips into the tops and sprinkle with flaky sea salt.
Bake in the preheated oven for 9-11 minutes, or until edges are golden brown.