To begin, preheat your oven to 350 and line a 9x9 pan with parchment paper.
In a large mixing bowl, add your coconut oil, brown sugar, and white sugar and cream them together with a hand mixer for a couple minutes. Add your peanut butter and blend it in till it's smooth. Lastly, add your vanilla and egg and lightly blend them in.
In a medium sized mixing bowl, add your gluten-free flour, cornstarch, baking soda and salt and stir them together.
Add your dry ingredients to your wet ingredients and stir them together till well combined, forming a smooth cookie dough. Gently fold your chocolate chips into the batter.
Pour your batter into your pan and carefully spread it out and around your pan, till you have one even layer of dough across the bottom of your pan.
Bake in the oven for 20-24 minutes, or till the top is set, the edges are turning more gold, and a toothpick inserted comes out clean. Gently shake your pan to check if the center jiggles still or not (they're done when there's no jiggle).
Let cool, then remove from the pan and slice into 12 bars. Devour!
Stored in an airtight container these cookie bars will taste best within 4-5 days.