Place the chocolate and the butter in a microwave-save bowl. Warm up in the microwave until the chocolate begins to soften -- don't microwave it too long, or your chocolate will burn. Once the butter and chocolate are melted, stir them together until well blended.
Add the condensed milk, and mix it well. Finally, add the drops of peppermint extract.
Line an 8x8 pan with aluminum foil, and then lightly butter the foil. Spread your fudge mixture into the pan evenly. Refrigerate until cool -- usually about an hour. Once the fudge has hardened, remove it from the pan and the foil, and cut into pieces. Store in an airtight container until it's all gone -- although that usually doesn't take long!
**Note -- if you're not a big peppermint fan, you can make plain fudge by eliminating the flavored extract, or try different flavors instead of the peppermint. Orange extract works nicely, as does rum and banana. You can also replace some of the chocolate with peanut butter chips, and make a peanut butter-chocolate fudge swirl, or add nuts or candy chips.