In a large bowl, whisk together the flour, cocoa powder, sugar, baking powder, and salt until combined. In a medium bowl, whisk together the buttermilk, vegetable oil, vanilla extract, and eggs.

Pour the wet mixture into the dry and use a rubber spatula to gently stir together, stopping when there are still a few pockets of the dry mixture not yet fully mixed in. Add in the chopped chocolate chunks, and finish stirring everything together until there are no dry pockets of flour remaining. The mixture will be lumpy- you want to mix until it's just combined.

Cover with plastic wrap and let the mixture sit at room temperature for 30 minutes. Meanwhile, preheat your oven to 375 degrees and lightly grease a mini-muffin tin.

Once the batter has rested, fill your muffin tin cups so that the batter goes almost all the way to the top of each cup. Bake for 12-15 minutes, or until the muffins are puffed and a toothpick comes out mostly clean. I like to loosen the muffins from the tin gently while they are still hot, and then allow them to cool in the pan for about 15 minutes before removing to cool on a wire rack. Enjoy!