Prep the pan. Line an 8x8-inch baking pan with parchment paper, leaving overhang on two sides for easy lifting. Lightly grease the parchment to prevent sticking.

Combine the base. In a medium saucepan, add the chocolate chips, sweetened condensed milk, and butter. Keep the heat low to prevent scorching.

Stir gently. Warm the mixture, stirring slowly and consistently with a rubber spatula until the chocolate is almost melted and the mixture looks glossy. Remove from heat before it’s completely smooth; residual heat will finish the job.

Add flavor (optional). Stir in 1 teaspoon vanilla extract or a pinch of salt for balance. Fold in any mix-ins like chopped nuts or mini marshmallows.

Pour and level. Scrape the fudge into the prepared pan. Smooth the top with an offset spatula. If using, sprinkle flaky sea salt on top.

Chill to set. Refrigerate for 2–3 hours, or until firm enough to slice cleanly. Don’t rush this step; it ensures neat squares.

Slice and serve. Lift the fudge out using the parchment overhang. Use a sharp knife warmed under hot water and wiped dry for clean cuts. Cut into 1-inch squares.