Does adding water in the empty muffin cups really make a difference?
Using the blueberry muffin recipe from The Bread Bible, the unused empty muffin cups are half filled with water. According to Rose Levy Beranbaum, it “prevents the heat from being drawn to them and adds moisture”.
It’s not necessary to the final flavor, but it did effect the final look of the muffins and surface texture. As they say, a picture says a thousand words.