Preheat oven to 325 degrees F (165 degrees C). Line muffin cups with paper liners.
Melt together butter and chocolate chips. Stir and set aside to cool.
In a separate bowl, combine the eggs, vanilla, sugar and flour.
Add the butter chocolate mixture and stir together well.
Fill paper lined muffin pans 2/3 full. Bake at 325 degrees F(165 degrees C) for 25 minutes.