1 pound of white sugar
1 pound of brown sugar
5 T light corn syrup
3/4 c. milk
1 stick + 2 T butter
2 t vanilla extract
You will need an accurate candy thermometer. Once the fudge is cooked, there are two ways of finishing it, and you will need to decide which to do and prepare it before you start.
Method 1, using a marble slab and wooden or metal bars to contain the candy: Set the bars up in a square. Don't let the candy spread to too large a space; that makes it harder to work. But the square should be large enough that the candy will not overflow. Spread the slab (inside the square) with the butter.
Method 2, stirring it in the pan: put several inches of cold water in the sink.
Now, you are ready to cook the candy.
1. Put the first four ingredients in a pot large enough that the candy cannot boil over.
2. Over medium high heat, stir and cook until the mixture begins to boil, and then cook without stirring to 236 degrees Fahrenheit.
3a. If using Method 1, pour the candy out over the butter and let it cool a little. It is ready to work when heat from the candy does not feel very hot to your wrist, face, back of your hand or other part of the body less inured to heat than your fingertips. Add the vanilla. Remove the bars, and work the candy with a fondant paddle (or good-quality putty knife). Start at the edge, and with each curved stroke, work it to the center. Be sure to incorporate all the butter. The candy is ready when it becomes stiff and loses its shine.
3b. If using Method 2, remove the pot from the heat, and put it in the sink with water. Add the butter. (The extra 2 T are not necessary, as it can't drip off the edge of the slab if you're not using one.) Allow it to cool somewhat, then add the vanilla and stir vigorously until, again, the candy is stiff and loses its luster. Pour it out on a cookie sheet when it is barely liquid enough to pour. It will take a while, so dry the bottom of the pan and sit to stir, with the pan on your lap.
Fudge is excellent dipped in chocolate. Or spread it out half an inch thick or so and cut it into squares. Wrap whatever doesn't get eaten right away in plastic cling wrap to keep it from drying out.
The key to great peanut butter fudge-or any fudge, for that matter--is in the cooling process. While you do not want sugar crystals to form in most candies, you do want them to form in fudge. The crystals are very small, so they feel smooth on your tongue, instead of grainy.