In a large bowl, combine oat flour, cocoa powder, ground flaxseed, sugar, baking powder, baking soda, and salt.
Add peanut butter and non-dairy milk and stir well to form a dough. The dough should hold together and not be crumbly. If it's too dry, add extra non-dairy milk a teaspoon at a time. Rest the dough for about 10 minutes - it will be sticky at first, but after resting it should be easier to handle.
Place the dough between two pieces of parchment paper or silicone baking mats. Roll out into a rectangle about 1/16-inch thick. Cut into 1-inch squares (or whatever size you prefer). Separate the squares and arrange them on one of the baking mats so they aren't touching.
Place the baking mat on your sheet pan. Transfer to the oven to bake for 15-20 minutes until crisp. Check after 15 minutes - some crackers may cook faster than others, so remove these and continue baking the rest.
Cool completely on the pan before transferring to an airtight container for storing.
Notes
1) Sheet Pan Size: I developed this recipe using a toaster oven with a quarter sheet pan. If you are using a full sized oven, you can double the recipe and bake on a half sheet pan.