First line an aluminium foil or butter paper in a 6 x 6 inch square pan, the foil or butter paper has to cover all the sides.
Combine dark chocolate with the condensed milk and microwave.
Once all the chocolate is melted, quickly add chopped walnuts, butter, salt and vanilla extract or vanilla powder, stir very well, then pour the whole chocolate fudge mixture in the pan lined with aluminium foil.
Let the fudge cool at room temperature. do not cover the pan, once the fudge has cooled at room temperature, cover the pan and refrigerate the fudge for 2 to 3 hours or overnight, till it sets completely.
Later remove the chocolate fudge along with the foil and place it on a chopping board, slice the chocolate into squares. Serve these chocolate fudge or wrap them in foil or butter paper and keep covered in a jar or box in the fridge.