Preheat your oven to 180°C (350°F) and grease a brownie pan or line it with parchment paper.
Whisk the melted butter and brown sugar together until smooth.
Add in the egg and vanilla, stirring until fully combined.
Mix the flour, baking powder, and salt in a separate bowl, then fold it into the wet ingredients.
Stir in the chopped dark chocolate and milk chocolate chips.
Scoop the dough into the pan, spreading it evenly.
Bake for about 25 minutes or until the top looks set and a toothpick comes out with moist crumbs.
Cool before slicing, or dig in warm if you're impatient like me.