Preheat the oven to 350°F / 177 C (middle rack) and line mini–muffin tins with liners. (24 mini muffins pan) Spray liners with cooking spray.
Melt the butter and chocolate in large microwaveable bowl, 1 minute at 70%. Stir and continue melting with the same method, until it's all melted and combined. Stir after each one minute interval.
In large kitchen bowl, whisk together flour, cocoa, and salt, set aside.
Whisk in melted butter and chocolate granulated sugar. Add eggs, one at a time, whisking after each addition until well incorporated.
Stir in flour mixture and using wooden spatula, gently incorporate the flour.
Spoon the brownie batter into muffin liners, filling cups almost to the top. It will be about 1 tablespoon in each tint.
Bake in preheated oven to 350 F / 177 C ,for 10-12 minutes, or until the brownie cupcakes top is set.
Cool for 5 minutes in tins and turn out onto kitchen counter.
Place it on white plate and dust with confectioners sugar if desired.