Preheat the oven to 400° F with the rack in the upper third of the oven. Grease muffin pans with butter or line muffin tins with paper liners.
In a large mixing bowl whisk together the gluten free all-purpose flour, millet, baking soda, baking powder, and salt.
In a separate bowl combine the yogurt, eggs, butter, coconut sugar, orange juice, and zest, whisking well until the mixture is smooth.
Add the wet ingredients to the dry ingredients and stir until everything is incorporated. Add the blueberries and gently fold into the batter until just incorporated. The batter will be thick.
Divide the batter among the muffin cups, filling each one to just slightly below the rim.
Bake for 15 minutes or until the muffin tops are slightly browned and a toothpick inserted in the center comes out clean. Let cool in the pan for a few minutes then turn the muffins out of the pan to cool completely on a wire rack.