Bring a large saucepan of water to a boil over medium heat.
Combine cheeses & roll into large balls.
Place a sheet of pasta on a floured work surface. Place cheese ball onto pasta & lightly press with a glass. Using a spoon, create a well.
Carefully add egg yolk to well. Cover with another sheet of pasta & using a large cooke cutter, pizza cutter or glass, cut & seal.
Boil ravioli for 3-4 minutes, flipping halfway through. Remove with a slotted spoon.
Serve with a touch of pasta water & drizzle with melted butter. Garnish with fresh grated parmesan.