Preheat the oven to 350. Cover the bottom of a (9in) round baking pan with wax paper, and cover with butter and sugar the sides (or the whole thing instead of using wax paper. You can buy pre-cut wax paper bases in specialized kitchen stores).
In a big bowl with a standing mixer, mix the eggs (whole) with a little bit of the sugar, for a long time, until they multiply in volume (15 minutes or so).
Meanwhile, grind the nuts with most of the remaining sugar in a food processor. (Note: you can buy hazelnuts without skin, though they are more expensive. Hazelnuts with the skin are perfectly fine, you don't have to take it off, which is complicated.)
When the eggs are fully whipped, incorporate the ground nuts and some spice, as desired (I use cinnamon and nutmeg, and a touch of cloves. If you like some heat, you can also use pepper, as well as hot peppers - but of course not everybody likes hot pepper, especially in cakes).
Pour the mixture into the baking pan and bake for 40 minutes or so, until a tootpick inserted into the cake comes out clean. Carefully remove from the pan (the cake breaks easily, it does not have the structure of wheat based cakes). Keep covered in plastic, as the cake will dry if left uncovered in a dry place.