Preheat oven to 350°. Line a muffin tin with 12 liners.
In a medium bowl, whisk together flour, cocoa powder, baking soda, baking powder, and salt.
In a large bowl, combine melted butter, sugar, sour cream, vanilla, eggs and applesauce.
Combine wet ingredients and dry ingredients. Fold in chocolate chunks or chocolate chips with a rubber spatula.
Scoop batter into paper muffin liners. Bake for 15 minutes.
Sprinkle a few extra chocolate chunks or chocolate chips onto each muffin as they get out of the oven. Press lightly into each muffin.
Let cool 5 minutes before transferring muffins to a wire rack.