Line a 4 x 7-inch microwave safe dish with parchment paper and set aside.
In a microwave safe bowl, add the melted butter and half the chocolate and microwave until melted. Whisk in the superfine sugar until combined. Add the warm milk and flour and whisk together until smooth. Fold through the remaining chocolate.
Transfer the brownie batter into the microwave safe dish and microwave for 1 1/2 minutes, until the tops are mostly cooked.
Remove the brownies from the microwave and let them cool completely, before slicing and serving.
Notes
* Use a chopped up chocolate bar (I used Lindt 70%) or chocolate chips. ** To heat treat flour, spread the flour on a lined baking sheet and bake in the oven at 180C/350F for 5 minutes. Remove the flour from the oven and let it cool completely, before using it. TO STORE: Cover the dish and store them in the refrigerator for up to 2 weeks.TO FREEZE: Place leftovers in a shallow container and store them in the freezer for up to 6 months.