Generously butter an 8x8 baking dish and set aside.
Lightly dampen a pastry brush and keep nearby the stove.
In medium-sized saucepan combine sugar, milk, corn syrup and chocolate over medium heat.
Using a wooden spoon, stir constantly, occasionally brushing the side of the pot with the pastry brush to remove crystals that might fall into your fudge.
Once mixture begins to boil, attach your candy thermometer to the pot (make sure the bottom of the thermometer isn't touching the bottom of the pan).
Stir mixture occasionally until your thermometer reads 238F (soft ball stage).
Immediately remove pan from heat and add your butter and vanilla extract. Do not stir the butter and vanilla! Allow it to set and melt
Leave mixture undisturbed until your candy thermometer reads 110F.
Now, using a clean wooden spoon, begin to stir the mixture vigorously (be careful not to scrape the sides or you may knock sugar crystals into the fudge, causing grainy fudge) until it begins to lose its shiny sheen and thicken (It will take a good bit of stirring before the fudge is just right, your arms will get tired and it's not a bad idea to have a back-up stirrer... seriously!)
Immediately once the fudge begins to thicken pour into prepared 8x8 pan.
Allow to cool completely before cutting and serving.
*Please see notes in post for tips and best results
Serving: 1piece | Calories: 99kcal
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