1 medium yellow onion, halved
1 whole chicken, 3 to 4 pounds
1 beef short rib (la costola in Italian)
2 medium carrots, peeled
2 medium celery stalks, trimmed
2 fresh bay leaves
1 leftover rind Parmigiano-Reggiano
1 teaspoon whole black peppercorns
Flaky sea salt
Blacken the onions.
Heat a small skillet over high heat. Place the onion halves, cut side down, in the skillet and cook, undisturbed, until blackened on the bottom, about 15 minutes. Remove the skillet from the heat and place the onion halves in a large stockpot.
Place the chicken in the stockpot with the onions. Add the beef rib, carrots, celery, bay leaves, and Parmigiano rind. Place half of the peppercorns on your cutting board and crush lightly to crack open. Add the cracked and whole peppercorns to the stockpot along with enough cold water to cover all the ingredients.
Place the stockpot over high heat and bring to a boil. Reduce the heat to maintain a gentle simmer, and cook until reduced by a third, up to six hours (or until the vegetables lose their flavor). Every 10 to 15 minutes, use a spoon to skim off and discard any impurities from the surface of the bubbling broth.
When the broth is ready, remove it from the heat. Remove and discard the meat and large vegetables.
Strain the broth slowly into another saucepan. Taste the broth, and season with salt.
To cook the tortellini, bring a medium saucepan of broth to a boil. Add enough tortellini as will fit with plenty of room to move around and cook, stirring occasionally, until they float to the surface. As soon as they float, using a slotted spoon, lift the tortellini from the broth and transfer to bowls. Spoon the hot broth over the tortellini, enough to just cover it, and serve.