Preheat oven to 375º F. Place millet in a spice or coffee grinder and grind slightly (not all the way to flour). If you don’t have a spice grinder, a small blender or food processor will work.

Combine sugar and egg in a large bowl; beat to combine. Stir in buttermilk, millet, and butter.

Combine flours through cinnamon in a separate bowl and stir to combine. Add these dry ingredients to the millet mixture; mix until moistened. Stir in apple pieces.

Scoop batter into 12 greased or sprayed muffin cups. Bake at 375°F for 15–18 minutes, until muffins spring back slightly.