Boil the potatoes in their skins. When cool, peel them and puree them with a potato ricer in small bowl. Heat olive oil in a small pan and sauté the onion for a few minutes to soften. Add the potato puree with some salt and pepper. Mix the egg yolk, herbs and parmesan.
With a round cutter approx. 7cm in diameter cut the pasta in batches to prevent drying out. Place a small ball of mix on centre of each pasta round, fold in halves and seal with dampened fingers. Bring each corner together and press.
When the tortellini are made, bring a large saucepan of water to the boil. Add salt, then gently slide in half the tortellini, and cook for 4 minutes. When the pasta rises to the surface remove it with a slotted spoon and transfer it to a pan with melted butter and fry over heat until the butter goes a golden brown colour.
Meanwhile, heat another pan and cook the baby beets until heated in butter.
Place the tortellini on a long rectangular plate, and scatter some of the beets and the Persian fetta around the plate. Sprinkle the plate with some of the golden butter and a pinch of cinnamon.