Place all filling ingredients into a mixing bowl and mix together until completely combined. Cover and refrigerate until ready to use. Lightly flour a surface and roll out the pasta dough until transparent. (Your hand will be visible through the pasta) Cut eight 4x6” rectangles of dough and brush the tops with the egg wash. Place 2 heaping spoonfuls of the filling in the center of one rectangle, leaving at least a ½” border. With the back of your spoon, create a shallow crater in the center off the filling, and add one egg yolk. Fold the other side of the pasta on top of the filling, and gently press down the sides, making sure to burp out any air bubbles. With a dusted round pastry cutter or biscuit cutter, cut the square ravioli into a round ravioli. Again, gently seal the edges.
Fill a large pot with water, add salt, and bring to a rapid boil. Turn the heat down just below a simmer to poach. Add the ravioli gently to the poaching water and cook 5 to 6 minutes. While the ravioli are poaching, brown your butter. Cook slowly in a pan until browned and toasted. Add a pinch of Cook’s Line Seasoning or your own salt and pepper. Remove the ravioli with a slotted spoon, shaking off excess water. You may need to dab with a towel… water on the plate is not good eats. Top the ravioli with caramelized shallots and prosciutto, and drizzle with brown butter. Garnish with parsley.