dry roast coconut flour and oats flour in a pan (I used homemade oats flour in this recipe).
In a large bowl using a hand mixer or stand mixer, cream together the powdered sugar, milk and butter. Beat until fluffy and light in color, about 1 minute. add vanilla extract if you like.
Add both the flours and Beat in flour until just combined. Add milk or water one tablespoon at a time and beat until dough starts to come together.