Rich, creamy, decadent Nutella fudge made with white and dark chocolate and toasted hazelnuts.
Toast the hazelnuts. You can do this on the stovetop by placing the hazelnuts in a saucepan on medium heat, tossing every 30 seconds or so until the nuts are fragrant. Alternatively, put the hazelnuts in the oven on a sheet pan and roast for 8 minutes at 350°F/180°C (toss halfway through). Allow the nuts to cool completely. Then, rough chop them in the food processor or using a large knife and cutting board.
In a heatproof bowl in the microwave, melt sweetened condensed milk, butter, and Nutella. Transfer half of the mixture into another heatproof bowl. Add bittersweet chocolate to one bowl and white chocolate to the other bowl. Microwave each bowl in 30-second increments, stirring after every 30 seconds (to prevent overheating) until melted and smooth. Stir in half of the hazelnuts into each bowl. Work quickly to avoid the mixtures from becoming muddy.