1 pound ricotta
1/2 cup plus 2 tablespoons all-purpose flour plus more
1 large egg, beaten to blend
1 1/4 cups finely grated Parmesan
3/4 teaspoon freshly grated nutmeg
1/2 tablespoon kosher salt
10 cups low-salt chicken broth
2 pounds skinless, boneless chicken thighs
1/4 cup (1/2 stick) unsalted butter
6 tablespoons all-purpose flour
2 celery stalks, cut crosswise into 1/4"-thick slices
1 carrot, peeled, thinly sliced
1 parsnip, peeled, cut into 1/4"-thick rounds
1 leek, halved lengthwise, cut crosswise into 1/4"-thick slices
1/4 cup chopped flat-leaf parsley
1/4 cup chopped fresh chives
Kosher salt, freshly ground pepper
Shaved Parmesan
Special equipment: Cheesecloth (optional)