Preheat oven (electric cooker: 140 °C/circulating air: 120 °C/gas: see manufacturer). Line baking tray with baking paper.
Coarsely chop the hazelnuts. Put the oat flakes, cocoa and nuts in a bowl. Warm the nut nougat cream slightly. Add honey and nut nougat cream to the flake mixture and mix well.
Spread on the sheet. Roast in a hot oven for about 50 minutes, stirring several times. Let it cool down. Roughly chop the chocolate and mix in.
Pack the finished muesli in airtight jars or storage tins. This way it stays crunchy for longer and keeps for at least 4 weeks.