Mix dry ingredients. Whisk egg, zest milk and melted butter. Stir in dry ingredients. Stir in blueberries. Fill Muffin tins 2/3 full. Bake 20 minutes at 400 degrees F or 200 degrees C.
While baking, combine second amount of butter with lemon juice. Put second amount of sugar in a bowl.
When muffins are slightly cool, dip tops into lemon butter then sugar.