Place the ground/milled flax in the bowl for your stand mixer (or a regular mixing bowl). Add the hot water to the flax in the bowl and let sit for 10 minutes.
Add coconut oil, brown sugar, granulated sugar, and vanilla to the flax mixture in the stand mixer bowl. Using the paddle attachment, mix on medium speed for a few minutes until creamy and fluffy. (If you don’t have a stand mixer, you can do this by hand with a mixing bowl and hand mixer or spoon).
Add the flour, cornstarch, baking soda, and salt. Mix on low speed until combined. (Note - If the dough is too dry at this point*, add in 1 to 2 tablespoons of dairy-free milk to reach the correct texture.)
Fold in the chocolate chips.
Use a small cookie scoop or heaping tablespoon to portion out balls of dough onto a plate. Cover with plastic wrap or foil, and chill in the fridge for at least 1 hour.
Preheat oven to 350 degrees F. Line two baking sheets with parchment paper. Remove cookies from the fridge and place on the parchment-lined baking sheets.
Bake for 9 to 12 minutes, until lightly browned and cooked through. Let cool for 10 minutes on the pan, and then enjoy!