Knead all ingredients into a dough and rest in a plastic bag. Peel the potatoes, cut into quarters, soften in salted water and strain. Fry onions in butter until golden and mix with the remaining ingredients of the filling.
Sauté shallots in butter, carrots and tender wheat, add beef broth and simmer until liquid is evaporated.
Chop arugula and whisk into butter.
Cook Tascherln in salted water, serve with tender wheat, sprinkle with Parmesan and pour over arugula butter.
Our tip: Fresh chives are much more aromatic than dried ones!