Line an 8x8-inch square baking pan with parchment paper. Set aside.
Place the Nutella and chocolate into a large microwave-safe bowl, and heat in 30 second intervals, stirring after each one, until melted and smooth.
Stir in the condensed milk and vanilla until combined. The mixture will be very thick.
Spread the mixture into the prepared pan, and smooth out the top. Refrigerate for 2 - 4 hours or overnight until completely set.
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Notes
Fudge can be stored in an airtight container in the fridge for up to 2 - 3 weeks. It also freezes well for up to 2 months. Thaw overnight in the fridge before serving.Nutella fudge will become quite soft when left at room temperature for too long.