Preheat your oven to 350 and line two pans with parchment paper.
In a large mixing bowl, add your coconut oil, peanut butter, brown sugar and white sugar and cream them together with a hand mixer for a couple minutes. Next, add your vanilla and egg and lightly blend till completely incorporated.
In a separate mixing bowl, add your dry ingredients and stir them together (gluten-free flour, cornstarch, baking soda, and salt).
Add your dry ingredients to your wet ingredients and stir them together till you have a smooth, thick cookie dough batter.
Scoop your cookie dough out onto your pan, using a cookie scoop. Using a fork, gently press down on each cookie twice, in a crisscross pattern (to flatten the cookie out).
Bake in the oven for 10-12 minutes, or till the edges of the cookies are set but the center may be a touch underdone.
Let cool on the pan for 10-15 minutes, and then move onto a cooling rack till entirely cooled.
These cookies taste best within the first 4-5 days.