Oil a 9″ (23 cm) long rectangular baking form, then cover its bottom and sides with baking paper. The baking paper needs to stick out at least 3/4″ (2 cm) above the walls.
Melt the butter in a suitable container on the stove and add the chocolate. Stir on low heat until homogenized and transfer to a bowl. Add the sugar and slightly beaten eggs, next the flour and cocoa. Pour the mixture into the prepared form. Bake in a moderately preheated oven about 35 min. Leave it to cool in the form.
For the white fudge, melt the butter with chocolate on low heat, then add the condensed milk and liqueur. Stir until the mixture becomes smooth and pour this over the brownies. Optionally you can put a little melted chocolate on top and use a skewer to make stripes.
Cover the form and put it in the fridge to harden. Then release the brownies from the form.
Also try cocoa brownies, vegan brownies, brownies with chocolate, brownies with walnuts, brownies with hazelnuts.