Preheat the oven to
180 deg C.
Cream together the butter and sugar until light and creamy. Slowly
add the egg yolks, mixing well.
Add the vanilla, grappa,
salt and lemon zest and
mix well. Add the flour and
mix to a soft dough.
Take teaspoons of mixture and gently roll them into balls. Place
them on baking parchment, gently flattening them with your hands.
Push a hole into the middle of each with the tip of your finger.