Prepare an 8x8 inch baking pan by greasing it or lining with parchment paper.

Combine granulated sugar, corn syrup, cocoa powder, chopped chocolate, salt, and half and half in a heavy-bottomed pot over medium heat.

Allow the mixture to come to a gentle boil and reach 235°F, the softball stage, monitoring closely with a candy thermometer.

Cool the mixture undisturbed until it hits 110°F, about 30 minutes.

Stir vigorously until the fudge thickens and loses its glossy sheen, around 5-10 minutes.

Pour the thickened fudge into the prepared pan and spread evenly.

Let the fudge set at room temperature for at least 2 hours.

Use parchment paper to lift the fudge out and cut into squares for serving.