Carefully pour the wet ingredients into the dry and stir just until combined using a rubber spatula in a folding motion. Do not over stir! Batter will be thick due to the sour cream. Fill muffin tin wells full with batter and place in the oven Immediately lower the temperature to 375 degrees and bake for 15-20 minutes or until an inserted toothpick comes out clean.
For The Glaze
While muffins are baking, make your glaze by whisking together ingredients. If you want a thicker glaze, add more powdered sugar or less milk. Brush onto muffins when they come out of the oven and sprinkle with coarse sugar if desired.