Line an 8×8-inch baking pan with parchment paper, leaving an overhang for easy removal.

In a medium saucepan over low heat (or a microwave-safe bowl), combine chocolate chips, sweetened condensed milk, and butter.

Stir constantly until smooth and glossy — about 5 to 8 minutes on the stove, or microwave in 30-second bursts stirring between each until smooth (about 1 to 2 minutes total). Tip: Use low heat and patience to avoid scorching.

Remove from heat, stir in vanilla extract and a pinch of salt. Fold in nuts if using.

Pour the melted mixture into the prepared pan and smooth the top with a spatula. Sprinkle festive toppings now so they stick as the fudge firms.

Chill in the refrigerator for at least 2 hours, or until firm. For quicker setting, place in the freezer for 30–45 minutes.

Lift the fudge from the pan using the parchment overhang and cut into 1-inch squares. Let sit at room temperature for 10–15 minutes before serving so flavors mellow.

Line an 8×8 pan with parchment.

In a heavy-bottomed saucepan combine granulated sugar, milk, unsalted butter, and salt. Bring to a boil over medium heat, stirring until sugar dissolves.

Clip a candy thermometer to the pan and boil without stirring until it reaches the soft-ball stage (236°F / 113°C), about 10–15 minutes.

Remove from heat, add chocolate chips and vanilla. Beat vigorously by hand until the mixture loses gloss and thickens (5–10 minutes).

Quickly spread into the pan, cool, and cut once set.