Preheat the oven to 350°F and coat a 24-cup mini muffin pan with nonstick spray.
Set a small saucepan over low heat and add butter and chocolate chips. Melt, stirring often, until completely smooth. Remove from heat and pour into a mixing bowl.
Add the granulated sugar to the chocolate, stirring until fully combined. Stir in eggs one at a time, then stir in the vanilla.
Add the flour and salt and mix until all of the flour is incorporated. Make sure to scrape the sides and bottom of the bowl to ensure no flour is left behind.
Divide batter equally among muffin cups, using about 1 tablespoon batter for each.
Bake for 10 minutes. Let cool a few minutes in the pan, then use an offset spatula or spoon to gently remove the brownies and transfer to a wire rack to cool completely.
Nutrition information is an estimate based on online calculators and provided as a courtesy. Any nutritional information should be used as a general guideline only.