Preheat oven to 350º and grease mini muffin tin with coconut oil. Set aside.
In a large mixing bowl, whisk together brown rice flour and coconut flour. Set aside.
In a separate bowl, mix together peanut butter, water, egg, and coconut oil.
Add wet ingredients to dry ingredients and mix together with a spoon or a fork until thoroughly combined. If needed, knead the dough with your hands.
Pack dough into mini muffin tins, filling 3/4 full. They will not rise.
Bake for 18-20 minutes, or until the edges become golden brown.
Transfer to a wire rack to cool.