Ground nuts are a common substitute for flour on Pesach. Ground almonds are more ubiquitous, but it does not surprise me that some recipes would call for ground hazelnuts instead.
Incidentally, ground almonds or hazelnuts mixed with melted butter or margarine makes an excellent Pesahdik alternative to a graham cracker crust, and is also useful year-round as a gluten-free crust. I like to use it for key lime pie, which is one of the few pie fillings out there that can be made Pesahdik without modifications to the standard recipe.
Maneschewitz makes a macaroon pie crust for Pesah.
The problem with Key Lime Pie is that I never once saw condensed or evaporated milk with an acceptable Pesah hechsher. I could be wrong and maybe one of the heimishe companies makes it.
Ka mashma lan, from my grandmother, a”h, to make a crust with pistachios, sugar, potato starch and egg whites (She was Syrian, and made lots of desserts on Pesah with pistachios, walnuts, dates, etc.)
Rebdoniel: I haven’t try this myself but you should be able to evaporate milk by cooking off more than half of the liquid on a low flame without letting the milk come to a boil. This per my internet research… Good luck!
RebDoniel: Gut Moed, would you have any of your Grandmother’s recipes with all different kind of nuts, dates, etc. for Pesach and the whole year? I would love to make them!