Preheat your oven to 335°F and prepare a mini loaf pan, ramekin, or muffin cup by brushing with butter or nonstick spray.
Add the butter and chocolate to a small heat-safe bowl, and microwave in 15-second increments until melted and warm.
Add the cocoa powder and whisk it in.
Break an egg in a separate bowl and whisk. Take 1 tablespoon (about ¼ of the egg) and add it to the batter. Whisk it in.
Add the granulated sugar and brown sugar, and whisk for 1-2 minutes.
Sift in the flour and salt, and gently fold it in with a small rubber spatula or spoon.
Fold in the chopped chocolate or chocolate chips.
Pour the batter into the mini loaf pan.
Bake for 15-18 minutes until the brownie is set on the edges but soft in the middle. A toothpick inserted in the center should come out with sticky crumbs (but not wet batter).
Enjoy!