2 tablespoons (28 grams) unsalted butter, cut into pieces
1/8 teaspoon salt
1 teaspoon pure vanilla extract
Chocolate Fudge: Grease the bottom and sides of an 8 x 8 x 2 inch (20 x 20 x 5 cm) pan with about 1 tablespoon (14 grams) of room temperature unsalted butter. Set aside.
In a heavy 2 1/2 - 3 quart saucepan, place the sugar, chocolate, light corn syrup, and half-and-half. Over medium-low heat stir the ingredients, with a wooden spoon, until it comes to a boil. Cover the pan with a lid for about 2-3 minutes to allow the sides of the pan to wash themselves down and dissolve any sugar crystals. Remove lid and clamp a candy thermometer onto the side of the saucepan and, making sure it does not touch the bottom of the pan, boil the mixture gently (adjust the heat as necessary) until the temperature reaches the soft ball stage (236 degrees F) (113 degrees C). Do not stir or shake. (Wash down the sides of the pan with a pastry brush dipped in cold water if any granules form.)
Remove from heat and drop the 2 tablespoons of butter on top of the fudge, but do not stir the butter into the fudge. Allow the fudge to cool to lukewarm (110 degrees F) (38 - 43 degrees C). Remove the thermometer and add the vanilla extract and salt. Beat the fudge (you can do this by hand with a wooden spoon or with an electric hand mixer) until it begins to lose its shine and is nice and creamy. Pour into the prepared pan and let cool for several hours before cutting into squares.