Preheat the oven to 180 degrees C/350 F.
Combine the dry ingredients in a large mixing bowl: brown rice flour, buckwheat flour, coconut sugar, baking powder and baking soda.
In a separate mixing bowl, combine the wet ingredients: apple cider vinegar, flax egg, vanilla extract and coconut oil.
Add the wet ingredients to the dry and mix together until a crumbly mixture forms. Then, add the plant based milk and continue mixing to form a dough, using your hands if necessary.
Using around 2 tbsp dough per cookie, roll the dough into balls and press them down slightly on a baking tray lined with parchment paper. If you want to, you can add chocolate chips to the dough, but I added a large chocolate button in the middle of each cookie.
Bake in the oven for 10-12 minutes until golden brown, and leave to cool for around 5-10 minutes before eating.