Make the pasta dough: Pulse the flour once or twice in a food processor. Add the eggs and olive oil and pulse untilthe dough gathers around the blade, 40 to 60 seconds. Turn the dough out onto the counter and knead a few times, then shape it into a smooth ball. Wrap the dough in plastic wrap and let rest at room temperature, 30 minutes. (The dough can be made a day ahead and refrigerated; bring it to room temperature before rolling.)
Prepare the filling: Remove the mushroom stems and set aside for the broth; finely chop the caps. Heat the olive oil in a large skillet over medium heat. Add the chopped mushroom caps and season lightly with salt; cook until they release their liquid, about 2 minutes. Increase the heat to medium high and cook until the pan is dry and the mushrooms are golden brown, about 3 minutes. Transfer to a bowl and let cool completely, then stir in the ricotta, chives, parsley, parmesan, egg yolk and nutmeg.
Make the broth: Combine the reserved mushroom stems in a large Dutch oven with the porcini, onion, carrot, celery, parmesan rind, parsley and thyme sprigs, peppercorns, 1 teaspoon salt and the lemon zest. Add 10 cups cold water and bring to a boil, then reduce the heat to low and simmer until the broth is dark and reduced by half, about 1 1/2 hours. Strain through a fine-mesh sieve into a clean pot and season with salt; set aside.
Meanwhile, fill and shape the pasta: Cut the dough into 4 pieces. Working with 1 piece at a time (and keeping the other pieces wrapped), flatten and shape the dough into a 3-inch square with your hands. Dust a clean work surface with flour; using a floured rolling pin, roll out the dough into a 10-inch square, about 1/8 inch thick. Trim the edges so they are straight, then cut the dough into sixteen 2-to-2 1/2-inch squares. Place a heaping teaspoonful of filling in the center of each square. With damp fingers, lightly moisten the edges of the dough; fold the square diagonally to form a triangle, pressing out any air pockets around the filling. Bring the 2 opposite points of the triangle together around your finger to form a ring; lightly moisten and pinch the points together to seal. Transfer to a well-floured baking sheet as you go. Repeat to form the remaining tortelloni.
Bring a large pot of salted water to a boil. Bring the prepared mushroom broth to a simmer. Add the tortelloni to the boiling water. After they float to the top, cook until al dente, 3 to 4 more minutes. Divide the mushroom broth among 6 bowls. Drain the tortelloni in a colander, then divide among the bowls. Top with chopped chives and parsley.