Line a 9” square heatproof baking dish with a sheet of parchment paper, leaving a length of paper on each end to lift out the fudge after it sets up. Lightly butter the parchment paper.
Combine the sugar with the butter and evaporated milk in a saucepan. Cook over medium-low heat, stirring occasionally until the sugar has dissolved, about 8 to 10 minutes.
Raise the heat to medium and bring the sugar and butter mixture to a boil. Insert a candy thermometer and continue cooking, stirring almost constantly until the mixture reaches a temperature of 234-degrees.
Remove the pan from the heat, add the chocolate and stir until the chocolate is completely melted into the fudge base.
Add the marshmallow crème and blend it into the fudge.
Stir in the chopped pecans and the vanilla extract.
Pour the fudge into the prepared baking pan and spread to smooth it out.
Let the fudge cool and set up for several hours or overnight, covered after it has cooled completely.
Cut the fudge into small squares, about 1” each.