Butter a baking sheet with the butter, and sprinkle lightly with flour.
Beat the eggs, sugar, vanilla, salt and lemon juice until foamy. This should take from 10 to 15 minutes.
Slowly add remaining flour and beat for another 5 minutes.
Place teaspoons of dough on the buttered and floured baking sheet. Leave 1inch of space between the little cookies. Sprinkle a few aniseeds on top.
Leave the unbaked cookies at room temperature for the night. The following day bake them at the lowest possible heat for 10 to 15 minutes, or until they are done. These have to be almost dried rather than baked, like a good meringue.