Preheat oven to 350°F and spray a mini muffin pan with nonstick spray.
In a saucepan, combine water, butter, and cocoa powder. Bring to a gentle boil while stirring.
In a large bowl, mix flour, sugar, baking soda, and salt.
Add the cocoa mixture into the dry ingredients and stir to combine.
Mix in sour cream and egg until batter is smooth.
Fill each muffin cup about 2/3 full with batter.
Bake for 10-12 minutes or until a toothpick comes out clean. Let them cool slightly.