Preheat oven to 350°F. Line a 9x13 inch pan with foil. Grease it with butter so that the pastry does not stick. Put the pan aside
Pour melted butter into a mixing bowl, add cocoa powder. Stir it until smooth.
Combine the chocolate mixture with flour and sugar. Whisk it. Add eggs and vanilla extract. Stir care fully until combined.
Pour the pastry into the prepared pan and smooth out. Bake for25-30 minutes. For reliability, insert a toothpick into the center of the cake, and if comes out dry, then the brownie is done. Take the cake out from the oven, let cool slightly.
Meanwhile, prepare the icing. Mix milk, cocoa powder, butter and powdered sugar until smooth. Pour the resulting mixture over warm cakes. Put brownie in the refrigerator for 20 minutes to cool down
Once the dessert has cooled, cut it into small bars and serve.
