In a 2-quart saucepan, combine granulated sugar, cocoa powder, half and half, salt, and corn syrup. Whisk the ingredients together until smooth and well mixed.

Place the pan over medium-low heat and bring the mixture to a gentle boil, stirring occasionally to prevent burning.

Allow the mixture to cook without stirring until it reaches 240°F (soft-ball stage).

Once reached, remove the pan from heat to prevent overcooking.

Place the butter and vanilla extract on top of the hot fudge mixture, but do not stir. Let the mixture cool undisturbed for about 20 minutes.

Using a hand mixer on medium to low speed, beat the fudge mixture for 1 to 3 minutes until it thickens and loses its glossy shine.

Quickly pour or scoop the fudge into a buttered plate or dish, using a spatula to spread it evenly.

Allow the fudge to cool for about 20 minutes before cutting into one-inch squares for serving.