Prep your pan: Line an 8x8-inch (20x20 cm) baking pan with parchment paper, leaving overhang on two sides for easy lifting. Lightly grease the parchment.

Set up your ingredients: Measure everything before you start. Fudge moves fast once it melts.

Melt gently: In a medium, heavy-bottomed saucepan over low heat, add the chocolate chips and sweetened condensed milk. Stir slowly and continuously with a silicone spatula to prevent scorching.

Add marshmallows: When the chocolate is mostly melted and smooth, add the mini marshmallows. Keep stirring until they melt and the mixture looks thick and glossy. If using vanilla or butter, stir it in now. Don’t overheat.

Check texture: The mixture should be smooth, dense, and shiny. If there are a few tiny unmelted bits of marshmallow, that’s fine—they’ll melt from residual heat.

Transfer to pan: Scrape the mixture into the prepared pan. Use the spatula to spread it into an even layer, pressing gently into the corners.

Optional finish: Sprinkle a pinch of flaky sea salt on top for contrast. You can also press chopped nuts on top while it’s still warm.

Chill: Refrigerate uncovered for 2–3 hours, or until firm enough to slice cleanly. For faster set, you can chill in the freezer for 45–60 minutes, but don’t forget it there.

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

Serve or store: Enjoy right away or pack into airtight containers with parchment between layers.