In a bowl, add the cacao powder, melted coconut oil, sugar and hot water. Mix until combined.
Add the powdered milk, corn starch, baking powder and combine.
Slowly add the oat flour and mix starting with a spoon and then with your hands. Continue adding the flour until the dough is no longer sticking to your hands. You may need more or less oat flour, please add in increments.
Open the dough between two sheets of parchment paper using a rolling pin. The cookies should be about 1/4 inches thick (5-6mm).
Cut into your favorite shapes. Rework the dough and continue cutting until finished.
Place cookies on a baking sheet covered with parchment paper OR coated with butter/oil.
Bake at 156F (180C) for about 15-20 minutes.