Mix milk and ground flax in a small bowl and set aside for a few minutes to gel.
In a large mixing bowl, combine peanut butter and olive oil.
Add granulated sugar and brown sugar and whisk until well combined.
Add flax mixture, miso, and vanilla extract and whisk to combine.
Add oat flour, potato starch, baking soda, and baking powder. Mix until a thick, cohesive dough forms. Fold in chocolate chips.
Cover the dough and chill in the fridge for at least 30 minutes and up to 24 hours.Tip: If you're short on time, you can skip the chilling step, but I do think the cookies are more flavorful after resting.
Preheat oven to 350°F/180°C. Line a cookie sheet with parchment paper or a silicone baking mat*. Remove dough from fridge and let it come to room temperature.
Scoop about 2 tbsp of dough and roll into balls. Place on baking sheet with at least an inch of space between each dough ball. Slightly flatten into discs to help the cookies spread.
Bake for 10 minutes. Drop the cookie sheet a few inches from the top of the baking rack once to deflate the cookies (this helps form crackly tops), then remove from the oven.Tip: For perfectly round edges, take a cookie cutter, mason jar lid, or cup that's slightly larger than the cookies. Place it over the hot cookie and move in a circular motion on the cookie sheet to round out the cookie's edges. This must be done right when you take the cookies out of the oven, before the edges have fully set.
Let the cookies cool on the sheet for 3 minutes, then transfer to a wire rack to cool completely.
Notes
1) I used unsweetened and unsalted peanut butter. I recommend using a natural peanut butter that is just made from peanuts and maybe salt. More processed peanut butters like Skippy and Jif are very thick while natural peanut butter is more thin and runny. If your peanut butter is too thick, your cookies may turn out more dense.2) I used red miso since I like the stronger salty, umami flavor, but white, yellow, or awase miso is fine too.