Line an 8x8-inch square baking dish with parchment paper, leaving some overhang on the sides for easy removal later. Set aside.
In a medium saucepan, combine the granulated sugar, cannabis-infused butter, cocoa powder, and evaporated milk over medium heat.
Stir continuously until the mixture comes to a boil.
Once boiling, attach the candy thermometer to the side of the saucepan and continue to cook, stirring constantly, until the mixture reaches 234°F (soft-ball stage).
Remove the saucepan from the heat and stir in the vanilla extract and semi-sweet chocolate chips until the chocolate is completely melted and the mixture is smooth.
If using chopped nuts, stir them into the fudge mixture until evenly distributed.
Immediately pour the fudge mixture into the prepared baking dish, spreading it out evenly with a spatula.
Place the baking dish in the refrigerator and chill the fudge until set, about 2 hours.
Once set, lift the fudge out of the baking dish using the parchment paper overhang.
Place it on a cutting board and cut it into 16 equal pieces.