Preheat the oven to 350◦F. Grease a standard 9x5 loaf pan.
Whisk together the flours, oats, baking powder, baking soda, and salt in a medium mixing bowl.
In a separate bowl, whisk together the butter or oil, yogurt, milk, honey and egg. Pour the liquid ingredients over the dry ingredients. Gently stir and fold the ingredients until all the flour has been incorporated and a wet batter is formed. Be careful not to over-mix. Pour the batter into the prepared pan, spreading to the edges.
Bake in the preheated oven for 45-50 minutes. When finished, a toothpick inserted into the center should come out clean. Cool in the pan for 15 minutes.
Wrap cooled loaves tightly in plastic wrap and store at room temperature. For freezer storage, wrap in plastic and aluminum foil and frozen for up to three months