Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients (flour through nutmeg) in a medium bowl; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal.
Combine buttermilk, egg, and rind; stir well with a whisk. Add to flour mixture; stir just until moist. Gently fold in blueberries.
Spoon batter into 12 muffin cups coated with cooking spray. Bake at 400° for 20 minutes or until the muffins spring back when lightly touched.
Remove muffins from pans immediately, and place on a wire rack to cool.
Combine lemon juice and powdered sugar in a small bowl. Drizzle glaze evenly over cooled muffins.
Note: You can make these muffins up to 2 days ahead and glaze them the morning of the brunch.