Step 1

Preheat the oven and prepare pan: Preheat the oven to 350°F. Spray a 10-inch cast iron skillet with nonstick cooking spray.

Step 2

Prepare the flax "egg": Combine the flax with 2 1/2 tablespoons of water in a small bowl. Let stand for 7 to 10 minutes to thicken. (This will be used as an egg replacer in this recipe.)

Step 3

Combine the coconut oil and sugar: In the bowl of a stand mixer fitted with the paddle attachment (or using electric hand beaters), beat the coconut oil, brown sugar, and granulated sugar until smooth and combined. The mixture will be a little clumpy and grainy—that’s ok.

Step 4

Add the flax egg and vanilla: With the mixer running on low, slowly add the flax egg and vanilla and beat until combined, using a rubber spatula to scrape down the sides as needed.

Step 5

Add the dry ingredients: In a small mixing bowl, whisk together the flour, baking soda, cornstarch and salt. With the mixer on medium, slowly add the dry ingredients and beat until smooth. The dough will look like large pebbles at first, but keep beating and it will eventually become smooth and uniform in 2 to 3 minutes.

Step 6

Add the chocolate chips and transfer to the skillet: With a spatula, fold the chocolate chips into the batter, then scrape the mixture into the 10-inch cast iron skillet. Using your hands, press the dough evenly into the pan. Sprinkle the top with flaky salt.

Step 7

Bake the cookie: Bake for 20 to 22 minutes, or until outer edges are golden brown. The cookie will still feel soft and even a little wet to the touch, but it’ll firm up as it cools.