01 - Line an 8-inch square baking pan with parchment paper, allowing some overhang for easy removal.
02 - Combine the sweetened condensed milk and semisweet chocolate chips in a medium saucepan over low heat, stirring constantly until completely melted and smooth, about 3 to 4 minutes.
03 - Remove the saucepan from heat. Stir in chocolate-hazelnut spread until fully blended and the mixture appears glossy.
04 - Transfer the mixture to the prepared pan and smooth the surface with a spatula.
05 - Sprinkle chopped toasted hazelnuts and a pinch of sea salt over the top, if desired.
06 - Refrigerate the pan for a minimum of 2 hours or until the mixture is thoroughly set.
07 - Lift the set fudge from the pan using the parchment overhang and slice into 24 small squares. Serve chilled or at room temperature.