Preheat oven to 400 degrees F. Line muffin tins with paper liners and set aside.
In the mixing bowl of a stand mixer, cream the butter and sugar together for 2-3 minutes.
Add the eggs, one at a time, mixing well after each addition. Add vanilla and mix well.
Fold in the chopped chocolate.
Scoop the batter into the lined muffin tins, filling them all the way to the top. Bake the muffins at 400 degrees F for 5 minutes.