If necessary, make pasta dough and roll into sheets. You shouldn't need much more than about 18 inches of rolled out dough.
The dough should be thin enough to see shadows through, but not so thin that it will easily tear. If using a rolling machine, a 4 setting is ideal.
Separate the egg white from the yolk, being very careful to keep the yolk intact.
In a mixing bowl, add ricotta, parmesan, chopped parsley, and ¼ teaspoon of salt.
Thoroughly mix together until combined.
Add cheese mixture to a piping bag (OR into the corner of a plastic ziploc bag). Place in fridge or freezer while preparing pasta.
Roll out one sheet of pasta (or roll the whole thing, then fold in half later). Make sure there is no excess flour on the top side of the pasta sheet.
Remove the cheese mixture from the fridge and, if using a ziploc bag, cut a small hole in the corner.
Take a 5-6 inch diameter round ravioli stamp, cookie cutter, or upside-down bowl and gently press into the pasta dough, to set your center.
In a small bowl, whisk the egg white and gently brush over the circle, covering it entirely.
In the center of the circle, pipe the cheese mixture into a spiral-circle about 2 inches wide. Then, pipe a "fence" around the edge of the circle by layering the cheese mixture.
This is so that the yolk stays in place.
Very carefully, add the yolk to the center of the cheese circle.
Gently take the second pasta sheet and place on top of the circle, making sure the entirety of the pressed circle is covered. Use your fingers to press all of the air out as you press the pasta sheets together to seal.
If you have a large ravioli stamp or circular cookie cutter, go ahead and cut out the raviolo.
If you are using a bowl, press the bowl down (upside down) to create a tight seal around the edge.
Then, use a knife or a ridged pasta cutter to cut around the edge of the bowl.
Bring a large pot of heavily salted water to a boil.
While waiting for it to boil, heat 2 tablespoons of salted butter in a pan over medium-low heat.
Slowly bring the heat up and continue to stir until the butter begins to foam and eventually starts to brown and smell sweet.
Once browned, immediately remove from the heat to prevent burning. Add another tablespoon of cold butter into the pan off the heat and stir to emulsify.
Gently lower the raviolo into the salted boiling water.
Cook for 1-2 minutes, or until the entire ravioli floats.
Remove from boiling water using a spider or a spatula and add to the brown butter sauce.
Gently toss and coat the raviolo in sauce.
Serve on a plate while still warm, spoon extra sauce over, and garnish with parsley or chives.
Cut into it, let that yolk run, and enjoy!