- 4 cups sugar
- 1 (12-ounce) can evaporated milk
- 16 tablespoons unsalted butter (2 sticks)
- 2 cups walnuts or pecans, toasted and chopped coarse
- 1 (8-ounce) jar Marshmallow Fluff
- 2 teaspoons vanilla extract
- 12 ounces bittersweet chocolate, chopped
- 8 ounces unsweetened chocolate, chopped
Line 13 by 9-inch baking dish with two pieces of foil, placed perpendicular to each other; let edges of foil overhang pan.
Bring sugar, evaporated milk, and butter to boil in large, heavy-bottomed Dutch oven over medium-high heat, stirring constantly. Reduce to simmer and cook, stirring constantly, until mixture is light tan in color and registers 234 degrees on instant-read or candy thermometer, 7 to 12 minutes.
Take pan off heat; stir in walnuts, Marshmallow Fluff, and vanilla until uniformly combined. Let mixture cool to 200 degrees, about 7 minutes.
Stir in chocolates until smooth. Pour mixture into prepared pan and refrigerate, uncovered, until firm, about 4 hours. Using foil overhang, remove fudge from pan and cut into squares. (Fudge can be refrigerated in airtight container for up to 1 month.)