Gather ingredients: 2 cups (340 g) semi-sweet chocolate chips, 1 can (14 oz / 397 g) sweetened condensed milk, 1/4 cup (60 g) unsalted butter, 1 teaspoon vanilla extract, pinch of salt
Optional add-ins: 1 cup chopped nuts and/or 1/2 cup mini marshmallows and/or 1/2 cup peanut butter chips
Line an 8×8-inch (20×20 cm) pan with parchment paper
Combine chocolate chips, sweetened condensed milk, and butter in a saucepan over low heat
Stir constantly until smooth and fully melted
Remove from heat and stir in vanilla and salt
Stir in optional add-ins
Pour mixture into the prepared pan and spread evenly
Refrigerate 2 to 4 hours until set
Lift out using parchment and cut into squares
Store in an airtight container in the refrigerator for up to 1 week or at room temperature for a few days