Divide the pasta dough into 2-3 sections. Work with one section at a time, keeping the remaining sections wrapped.
Use a rolling pin or a pasta machine to roll the dough as thin as possible. With a pasta machine, roll the dough on gradually smaller settings until you can roll it out on the thinnest setting.
Use a 3” round biscuit cutter to cut circles out of the rolled dough. Gather the scraps together, re-roll the dough and cut out additional circles. Keep the rounds covered with plastic wrap or a damp paper towel to keep everything moist. The dough will dry out quickly. Continue rolling out and cutting the dough.
Stir together drained ricotta, parmesan, salt, pepper, and parsley.
Place one teaspoon of the ricotta mixture in the center of each circle.
Use a pastry brush or your finger to moisten around the edge of the circle with water and then fold in half to form a half moon, sealing the filling in the center.
Fold the two points of the half moon back to meet each other and press the ends together to form the tortellini.
Continue for the remaining circles. Sprinkle with flour as needed to prevent pasta from sticking to the board or to the other tortellini.
Cook tortellini in a pot of salted, boiling water until it floats to the top. Or spread in a single layer on parchment paper and freeze; then, transfer to a freezer baggy or storage container and keep frozen for up to 3 months.