Martha'S Chocolate Fudge - cooking recipe

Ingredients

2 tablespoons unsalted butter, plus more for pan (not margarine)
3 tablespoons best-quality cocoa powder (Dutch process will give superior results)
2 cups sugar
2/3 cup whole milk (do not use reduced fat milk.)
3 ounces best-quality semisweet chocolate, finely chopped (baking chocolate)
2 tablespoons light corn syrup
1 teaspoon vanilla extract
1 cup walnut halves, cut into large pieces (optional)

Preparation

You will need a candy thermometer. Make your fudge on a dry day. Too much humidity will keep the fudge from setting up properly.
Butter an 8-by-8-by-2-inch pan and place it in the fridge. Alternately, use a loaf pan if you want really thick pieces.
Sift cocoa powder and sugar into a medium bowl.
Prepare an ice bath. I use my sink, filling it with approximately 2\" of water, then adding a bunch of ice.
In a small saucepan, combine milk and cocoa-powder mixture with a wooden spoon until a sandy, paste like texture forms.
Add chocolate, butter, and corn syrup.
Cook on med-low heat (don't let it boil yet), stirring constantly, until sugar has dissolved completely (very important), 7 to 10 minutes.
Using a pastry brush dipped in cold water, wash down any sugar crystals that form along the sides of pan.
Clip a candy thermometer to the side of the pan, making sure the tip of the thermometer does not touch the bottom of the pan.
Increase heat a bit until the fudge starts to boil. When the fudge begins to boil, stop stirring and don't stir AT ALL for the rest of the cooking time or the fudge will be grainy.
Keep the syrup boiling, being careful that it doesn't boil over.
When the candy thermometer registers 236\u00b0, remove the pan from heat, and place in ice bath for 5 seconds.
Transfer pan to a heat-proof surface, and let sit until thermometer registers 110\u00b0, about 45 minutes.
Add vanilla, and using a wooden spoon (or electric hand mixer), stir fudge briskly until it thickens and begins to lose its sheen, 2 to 3 minutes (it may take a little longer to set up. Depending on the humidity in the air, it could take as much as 10 minutes).
Stir in walnuts, if desired.
Spread fudge into prepared pan with wooden spoon. Cover with plastic wrap; chill 30-60 minutes. Cut into 1-inch squares.