Prepare all ingredients:
Bake the potatoes in robe des champs.
When finished, peel them and smash them to obtain a light purée.
Add the egg yolks, sugar, powdered hazelnuts, flour, cinamon and the grated zests of the lemon.
Beat the egg whites firm...
...and delicately add them to the mixture.
Butter a cake mold and pour the mixture in it.
Bake 35 minutes at 180°C.
Serve warm.