Preheat oven to 350°F. Grease a 24-cup mini muffin pan with non-stick spray.
In a medium saucepan, melt butter over medium heat. Stir in the sugar, followed by the cocoa powder and vanilla extract. Remove from heat and allow the mixture to cool.
Whisk in the eggs and salt and then gently stir in the flour and chocolate chips until just combined.
Scoop the batter into the prepared mini muffin pan, filling each cup about three-quarters full.
Bake for 12-15 minutes in the preheated oven
Allow to cool in the pan for 10 - 12 minutes before transferring to a wire rack to cool completely.