Line a 9 x 13 x 2-inch pan with parchment paper, leaving a 1-inch overhang on either side, and either butter or spray lightly with pan spray. You may forego the parchment paper, but it does help the fudge lift out of the pan more easily once it has fully set up.
Add 4 ½ cups granulated sugar, 2 tablespoons unsalted butter, 1 pinch salt, and 1 (12-ounce) can evaporated milk to a large saucepan and heat over medium-low heat, stirring until the sugar fully dissolves.
Increase the heat to medium and bring the sugar mixture to a rolling boil, stirring as needed to ensure it does not boil over. Boil for 6-8 minutes.
Meanwhile, add 12 ounces semi-sweet chocolate chips, 12 ounces German baking chocolate,7 ounces marshmallow fluff, and 2 cups chopped pecans or walnuts to a large bowl. Set aside.
Once the sugar mixture is done boiling, pour it into the bowl with the chocolate mixture.
Stir until all of the chocolate has melted and the marshmallow fluff is no longer leaving white streaks in the fudge.
Add the fudge to the prepared pan and smooth over the top. You will want to do this right away after everything is combined, as the fudge begins to set up quickly. Set aside and let the fudge sit for at least 2 hours before removing it from the pan and slicing it into pieces. I was able to get about 48 pieces.