While the milk/sugar is boiling, dump the chocolate in a bowl, mix it a bit and cut up the butter. Pile the butter on top of the chocolate so that when the timer goes off, you're ready to go! Make sure the butter is cold!
This is what the milk/sugar mixture looked like right before the timer went off. If yours is a lot more bubbly or frothy, no worries. Once the timer rings and the temp is 233 - 235, turn the heat OFF. If you have an electric stove, take the pot off the heat or it will overcook. Moving quickly, dump in the chocolate, butter, and splash in some vanilla. I never measure it but you can if it makes you more comfortable. Stir the chocolate mixture with a heavy spoon until it is glossy and thick, just a few minutes. Pour into a 13 x 9" pan and refrigerate until cool.
Here is a pan of fudge!! The whole process from start to finish takes less than 20 minutes. I usually line the pan with a long piece of tin foil to make removing the fudge easier. I just forgot when I made this batch.
You can also create different variations using the same recipe.
Peanut Butter Cup Fudge - Use one bag the semisweet chips, one bag milk chocolate and one bag bittersweet chocolate chips. Add a big bag of chopped mini peanut butter cups once the all the chocolate/butter has been added and has started to melt. Stir to incorporate but don't stir so much they dissolve.
York Peppermint Patty Fudge - Add a big bag of chopped York Peppermint patties to the pot after the chocolate/butter mixture has been added. Stir to incorporate but don't stir so much they dissolve.
Rocky Road Fudge - Add about 2 cups toasted walnut pieces and about 3 cups or so mini marshmallows to the melted chocolate right before it's ready to be poured into the pan. Stir it a bit to coat and then pour into the pan.
Dark Chocolate with Sea Salt Fudge - Add about a teaspoon extra fine sea salt to the pot at the same time you add the chocolate and butter.