Line an 8-inch square pan with parchment, leaving overhang for lifting.
Warm condensed milk and butter in a medium saucepan over low heat until just steaming.
Stir in chocolate chips and fine salt. Cook gently, stirring, until completely smooth.
Remove from heat. Stir in vanilla, then fold in nuts if using.
Spread mixture into the prepared pan and smooth the top. Sprinkle flaky salt if desired.
Chill until firm, about 2 hours. Lift out and cut into small squares.
Notes
Try swirling 2 tbsp creamy peanut butter into the warm fudge before chilling, or swap walnuts for toasted almonds. Store tightly covered in the refrigerator for up to 2 weeks, or freeze up to 2 months.This recipe is an original creation inspired by classic Easy Fudge Recipes for Everyone flavors. All ingredient ratios and instructions are independently developed.