In a small bowl, whisk together the oat flour, erythritol, cocoa powder, baking powder and salt.
In a large microwave-safe bowl, add the almond milk, coconut oil and vanilla extract. Microwave at 15-second intervals, stirring between each one, until the coconut oil is melted.
Dump the dry ingredients into the wet ingredients and stir together until fully mixed. Dump the dough onto some plastic wrap. Pat the dough into a ball, then form into a log shape. Wrap the dough with the plastic wrap, then form into a smooth log.
Refrigerate the dough for 1-1½ hours.
Preheat the oven to 350 degrees Fahrenheit and line a cookie sheet with parchment paper.
With a sharp knife, slice the log into cookies. The dough is slightly delicate, so the bottoms of some slices may crumble off. It's really easy to just stick it back on though!
Put the cookie dough rounds onto the prepared cookie sheet and bake for 11 minutes. The cookies will be sponge-like right now, but don't worry, they firm up as they cool!
When the cookies are completely cool, add the dark chocolate and cacao butter to a small microwave-safe bowl. Microwave at 30-second intervals, stirring between each one, until melted. Stir in the peppermint flavor. Dip the cookies into the melted chocolate, tap off the excess, then place back on the cookie sheet. Refrigerate until completely firm. Serve and enjoy! Keeps for ~5 days.