In a large microwave safe bowl, and a 4 cup Pyrex measuring cup works perfectly, combine the chocolate and condensed milk.
Microwave for one minute, then stir, then again for 45 seconds. Keep stirring until the chocolate is completely melted. Let it sit and cool a wee while and move on to the next step.
Line an 8 inch by 8 inch baking pan with tinfoil, leaving little handles on two sides so you can pull it out completely when the fudge is set.
Mix in the cup of M&M's minus what you need to put on top. I made these large squares, 25 in the pan, but this could easily be done in a 6 inch by 6 inch baking pan.
Count those M&M's out for the top. It's ok if they start melting, in fact it made them even better, the mint chocolate inside swirled around in the fudge and the crunchy outside gave it a fantastic texture.
Refrigerate 2 to 2.5 hours until it's set.
Using those foil handles, pull the entire block of fudge out.