Grease 12 standard muffin tins with butter.
Preheat oven to 400˚F (200˚C).
In a medium bowl, whisk together the milk, cream, eggs, salt, nutmeg, and pepper until smooth.
In another bowl, toss together the shredded Gruyère, Emmentaler, and 1/2 tablespoon flour.
On a lightly floured surface, roll the chilled dough into a large sheet about 1/8 inch (3 millimeters) thick.
Use a 3 1/2 inch (9 centimeter) round cutter (scalloped if available) to cut out as many circles as possible.
Bring together the scraps of dough. Re-roll and cut to make 12 circles in total.
Place each circle in a greased muffin tin, gently pressing down across the edges and sides to keep air bubbles from forming.
Sprinkle some of the shredded cheese (about 1 tablespoon) across the bottom of each tartlet.
Gently pour the milk mixture over the cheese to fill each tartlet.
Immediately transfer the pan to the preheated oven and bake until the tops are puffed and golden, about 25-35 minutes.
Allow to cool briefly before removing the tartlets from the muffin tins.
These Chäschüechli are best served warm.