FIRST; you'll need a 9x13 baking pan lined with parchment paper. It does not have to be exact, the more the better, ok to be bigger than pan..no baking involved. You will also need a fork and a small hot pad.
In a microwave safe dish... hint; glass bowl is easier to clean. Put your butter, Chocolate, and then condensed milk in the bowl. Put bowel in microwave on high for 3 min. With a fork stir the ingredients together THIS WILL BE HOT, use the hot pad. Stir till well combined and QUICKLY add to the 9x13 lined pan. Smooth out the cocolate as smooth as you can and then simply put it in the fridge for 1 to 1 1/2 hours to firm up. Sometimes I put it in the freezer for a few, just to quicken it along. When firm cut into any size pieces and enjoy.. Again this is RICH so be ready to follow it with some milk. :-)