I’m a bit lazy and buy my hazelnuts already toasted. But if you can’t find toasted hazelnuts or want to do it yourself then place hazelnuts on a baking tray and bake in a preheated oven on 180C for 5-10 minutes until toasted and fragrant. Make sure you keep a close eye on the nuts as they can burn easily. Alternatively place them in a dry cast iron fry pan (skillet) and toast over medium heat until toasted and fragrant. Don’t worry about rubbing off the hazelnut skins (too much work in my mind) they’re fine in the slice.