Chop the couverture and hazelnut nougat mixture and melt together over a water bath. Then let the mixture cool down lukewarm and stir into the whipped butter.
Peel and roughly chop the pistachios. Put a tablespoon of the nuts aside and mix the remaining nuts with the chocolate nougat butter. Scatter the remaining nuts over the top and cover everything and chill. To make the chocolate nougat butter spreadable, it should be taken out of the refrigerator about 40 minutes before serving.