Cut the chocolate into small pieces and mix with the condensed milk in a container with no adhesive coating. Of very low heat stirring the ingredients until the chocolate is melted and mixed with milk. Add the butter and remove from heat, stirring until the butter is melted. You'll notice how the mixture begins to separate the bowl and then add powdered sugar. When all ingredients are well blended Pour mixture into small rectangular pan so the cake to be around 2 - 2.5 cm. Flatten with a spoon and sprinkle with chopped nuts in large pieces. So putting cake in the freezer for 1 hour, cut into small squares of the size of a walnut. To separate the thus obtained small candy, put the pan for about a minute in hot water.