In a microwave safe bowl, take the semi sweet chocolate chunks and nuke for a min. Remove and whisk for couple of times. Then, again put it back for 30 secs.
Depending on your microwave you may need to micro for another 30 secs. But, be very cautious to confirm the chocolate is melted and not getting burnt.
Remove and whisk again for a smooth texture.
Add condensed milk and microwave for 1 min 30 secs. Whisk well to get a smooth sauce.
Prepare a plate and cover with aluminum foil. Grease with butter/ ghee. Pour the chocolate sauce over the prepped plate and refrigerate for at least an hour. Cube into smaller pieces and indulge in this sinful temptations.