Preheat oven to 350°F. Coat a 10-inch cast-iron skillet with cooking spray.

Whisk all-purpose flour, whole-wheat flour, baking soda, baking powder and salt in a medium bowl.

Place brown sugar, granulated sugar, butter and oil in a large bowl; beat with an electric mixer on medium speed until fluffy, about 3 minutes. Add vanilla and beat until combined, about 10 seconds. Add eggs, 1 at a time, beating until combined after each addition, about 20 seconds, stopping to scrape down sides as needed.

Add half of the flour mixture to the sugar mixture and fold in with a spatula just until combined. Add the remaining flour mixture and ¾ cup chocolate chips; fold until combined.

Press the dough evenly into the prepared pan. Top with the remaining ¼ cup chocolate chips. Bake until the top and edges are golden and the center is just cooked through, about 35 minutes. Let cool for 5 to 10 minutes. Garnish with coarse sea salt, if desired. Slice and serve warm.