Line a 9-inch square baking pan with parchment paper.

In a heavy-bottomed saucepan, mix the granulated sugar and cocoa powder.

Pour in the whole milk and add the unsalted butter; stir until the butter is melted.

Place the saucepan over medium heat and stir continuously until the mixture comes to a boil.

Using a candy thermometer, cook the mixture until it reaches 234°F (soft ball stage).

Remove from heat immediately once the correct temperature is reached.

Stir in the vanilla extract and chopped nuts, if using.

Quickly pour the fudge mixture into the prepared baking pan and spread it evenly.

Let it cool at room temperature until set.