Place the flour, butter, Gruyère, and salt in the bowl of a food processor. Process just until the dough gathers into a ball. If the dough is crumbly, add a small amount of cream and process briefly again. The dough will be very soft and sticky.
Turn the dough out onto a well-floured board. Using a well-floured rolling pin, roll the dough to a thickness of 1/8 inch. Cut 2 inch round disks from the dough. Transfer the disks to a non-stick baking sheet.
Lightly brush the disks with the egg yolk mixture. Place a pinch of mimolette in the center of each disk. Top the cheese with a small grind of black pepper.
Bake the disks until crisp and browned, about 20 minutes.