Line an 8x8 inch square pan with aluminum foil or parchment paper, leaving an overhang on the sides. This will make it easy to lift the fudge out later. Grease the foil or parchment paper with butter or cooking spray to prevent sticking.

In a heavy-bottomed 3-quart saucepan, combine the sugar, butter, and evaporated milk. Make sure the saucepan is heavy-bottomed to prevent the fudge from scorching.

Cook over medium heat, stirring constantly, until the butter is melted and the sugar is dissolved. Continue cooking, stirring occasionally, until the mixture reaches a soft ball stage. This means that if you drop a small amount of the mixture into cold water, it should form a soft, pliable ball. Use a candy thermometer to monitor the temperature; it should reach 235-240°F (113-116°C).

Once the mixture reaches the soft ball stage, remove the saucepan from the heat immediately.

Add the chocolate chips, marshmallow creme, salt and vanilla extract to the hot mixture. Stir until the chocolate is completely melted and the mixture is smooth and creamy. Be patient, this might take a minute or two.

Stir in the chopped pecans until they are evenly distributed throughout the fudge.

Pour the fudge mixture into the prepared pan and spread it evenly with a spatula.

Cover the pan with plastic wrap and refrigerate for at least 2 hours, or until the fudge is firm and set.

Once the fudge is firm, lift it out of the pan using the foil or parchment paper overhang. Cut the fudge into small squares with a sharp knife.