Preheat the oven to 400F.
If your baking pan is not non-stick, lightly brush the holes with oil or melted butter (I don’t use oil in aerosol cans).
In a bowl, sift together the flour, sugar, baking powder and salt. Stir in the orange zest.
Make a well in the center of the dry ingredients and pour in the melted butter, milk and egg. Stir just until moistened, about 10 strokes. Overmixing yields tough and rubbery muffins.
Fold in the blueberries.
Spoon the mixture into the holes of the pan, filling each hole halfway.
Bake at 400F for 12 minutes.
Cool in the pan for about five minutes.
Place a rack on a tray. Move the muffins to the rack.
Meanwhile, make the glaze by stirring together the confectioner’s sugar, milk and orange juice until thick but pourable. Using a spoon, drizzle over the still warm muffins, allowing the excess to drip off into the pan.