Prepare the pasta dough according to the recipe and set aside, wrapped in plastic, while you prepare the stuffing
In a large stockpot, cover the potatoes with water and bring to a boil. Cook until they are easily pierced with the end of a paring knife, about 15 minutes. Drain
and, when cool enough to handle but still hot, peel
them and run them through a food mill
. Set aside.
Combine the onion and pancetta
in the bowl of a food processor
until both are finely chopped and mingled. In a 12 to 14-inch saute pan, heat the olive oil over high heat and add the pancetta and onion mixture. Cook for 5 minutes over high heat, then stir in the potatoes
and season with salt and pepper, to taste. Remove from the heat and turn the mixture into a large bowl. Mix in the egg yolks, chives, marjoram and 1 tablespoon grated Montasio. Set aside to cool.
Unwrap the pasta
dough and, using a pasta rolling machine, roll it out to the thinnest setting. Cut 3-inch squares from the dough. Using a spoon or clean hands, place walnut-sized dollops of the potato mixture onto half of the squares, and top them with the other squares to form the ravioli. Seal the edges of each raviolo and place them on a baking sheet.
Bring 6 quarts of water to a boil and add 2 tablespoons salt. Cook the ravioli in the boiling water until cooked through and tender, about 4 to 5 minutes. You may need to work in batches.
Meanwhile, in a 12 to 14-inch saute pan, heat the butter over medium-high heat until it foams, subsides, and begins to brown. Add a splash of the pasta cooking water. Add the cooked ravioli
to the pan and toss gently over high heat for 1 minute. Sprinkle with the poppy seeds
and remaining cheese
and serve immediately.