Remove the leaves from the florets until they can no longer be separated intact. The remaining firm florets can then be used for another Brussels sprouts dish. Blanch the leaves in salted water for five minutes and rinse in cold water.
Mince the hazelnuts with a meat mallet. Brown the butter in a pan at medium temperature and then brown the hazelnuts in it.
Finally, toss the well-drained Brussels sprouts leaves in the hazelnut butter until they are warm again.