On a clean work surface, mound the flour into a circle and create a well in the center.

Crack the eggs into the well, add salt and olive oil, then use a fork to beat the eggs and draw flour from the edges until roughly combined.

Knead the dough by hand for about 10 minutes until it is smooth, elastic, and slightly sticky, adding warm water one tablespoon at a time if too dry.

Wrap the dough in plastic wrap or cover with an inverted bowl and let it rest at room temperature for 15 minutes.

While the dough rests, combine the ricotta, Parmesan, parsley, egg yolk, nutmeg, salt, pepper, and lemon zest in a bowl and mix gently.

Divide the rested dough into quarters, keep three portions covered, and flatten one quarter into a thin disk.

Roll the disk with a rolling pin or pasta machine until it is about the thickness of a dime.

Use a 2.5 to 3 inch cutter to cut circles from the dough, place 1 teaspoon of filling in the center of each, wet the edges, and fold into a half moon to seal.

Bring the two pointed ends of the half moon together and press to form the tortellini shape, then place on a floured baking sheet; repeat with remaining dough.

Bring a large pot of generously salted water to a rolling boil, then add the tortellini and cook until they float plus 2 to 3 minutes.

While the tortellini cook, melt the butter in a large skillet over medium heat, add the sage leaves, and sauté for 2 to 3 minutes until fragrant and browned.

Use a slotted spoon to transfer the cooked tortellini from the water directly into the skillet with sage butter, toss gently, then season with Parmesan, salt, and pepper before serving immediately.