Combine the oat flour, almond flour, coconut sugar, salt, coconut oil, maple syrup, apple cider vinegar, vanilla extract, cinnamon, and nutmeg in a bowl or food processor. Mix until it starts to form a large ball. Check the moisture level by breaking off a small amount of dough. If you can roll it into a ball in your hands without it sticking too much, then it's perfect. If it's too wet, add more oat flour, 1 tablespoon at a time, until it's less sticky.