- 4 tablespoons (1/2 stick) unsalted butter, plus more for pan
- 3 cups mini marshmallows
- 1 cup sugar
- 1/2 cup heavy cream
- 1/2 teaspoon salt
- 1/2 teaspoon pure vanilla extract
- 1 bag (12 ounces) semisweet chocolate chips
- 1 cup walnuts, coarsely chopped
- Butter an 8-inch square baking pan; line with 2 crisscrossed pieces of parchment paper, leaving an overhang. Butter paper.
- In a large saucepan, combine butter, marshmallows, sugar, cream, and salt; cook over medium, stirring occasionally, until marshmallows are melted, 8 to 10 minutes. Off heat, stir in vanilla, chocolate chips, and 1/2 cup walnuts until chocolate is melted.
- Pour fudge into prepared pan, and smooth top; sprinkle with remaining walnuts. Let cool 30 minutes. Refrigerate until set, about 1 hour.
- Using overhang, lift fudge onto a cutting board; cut into squares (6 rows by 6 rows).
To store, refrigerate in an airtight container, up to 5 days.