Bring all the ingredients to room temperature so everything mixes together completely.
Use a large bowl and add the flax seeds, buckwheat flour, baking powder, salt, cinnamon and nutmeg. Mix everything together with a spoon.
In a medium bowl, add the egg, milk, vanilla, sugars and oil. Stir together.
All at once, add the liquid ingredients to the large bowl with the dry ingredients. Stir until everything is completely mixed. Stir in the grated apples.
This 30 minute period of time gives the batter time to absorb the ingredients (liquid hydrates the flours) which will result in lighter textured and higher rising baked goods.
The easiest way to portion the muffin cups is to use a measuring cup to pour the batter in. You'll only fill 10 cups and each cup should be about ⅔ full.
Bake the muffins at 350 F for about 20 minutes (between 17-22 minutes, so 20 minutes is average).