Place 1 teaspoon of ricotta on a wonton wrapper. Carefully put 1 egg yolk on top of the ricotta; be careful not to break the yolk.
Dip your finger in a small amount of water and wet the perimeter of the wonton square. Using another wonton wrapper, cover the filling and gently press the two seams together. Push out any air bubbles.
Cook ravioli in a pot of gently boiling salted water for about 2-3 minutes, or until they float to the top.
Serve with browned butter, thyme and shaved Parmesan.