The way I see it, chocolate hazelnut desserts can go one of two ways. One option is to exercise restraint on a wealth of sweetness, richness, and fat, maybe emphasize the ingredients' bitter or roasted qualities. The other approach is to embrace them full throttle, come what may. Nutella, for instance, takes this route, with a hefty dose of palm oil along for the ride—come what may.
This ice cream also goes for excess over restraint, but with just enough delicate bitter flavors to make the hazelnuts extra hazelnutty and the chocolate more chocolatey. It's even more rich than Nutella but less oily.
How rich? A pound of hazelnuts per quart. By the time you grind the hazelnuts down and blend them with cocoa and sugar, you're left with a pint of gianduja, the Italian term for chocolate hazelnut paste before Nutella was ever a thing. Mix it with equal parts half and half and there you go: deliriously intense gelato. Keep those scoops on the small side.
I would not advise using the gianduja as a stand-alone recipe: it relies on cocoa rather than chocolate and is less creamy and more gritty on its own than you may like. I'd also recommend letting your ice cream sit on the counter for 10 to 15 minutes before scooping, both to get the most out of your gelato and to make it easier on your wrist.