Heat olive oil in a large pan over high heat. Add onion and carrots and cook until golden, about 5 minutes. Push to the edges of the pan and add sausage. Sear for 1 minute per side, then break apart and cook until no longer pink. Stir veggies back in. Season with ½ teaspoon each salt and pepper.
Stir in garlic and tomato paste. Cook, stirring often, for 3–5 minutes, until the paste darkens and smells fragrant. Lower heat if needed to prevent burning.
Sprinkle flour evenly on top. Stir constantly for 1 minute. Slowly add 1 cup chicken broth, stirring constantly until thickened and nothing is sticking to the base of the pan.
Add mixture to crockpot along with remaining broth, Italian seasoning, and fennel seed. Cover and cook on low 6–7 hours or high 3–4 hours.
Uncover and stir in tortellini, kale, and heavy cream. Cover and cook on high for 20 minutes, or until tortellini is tender. Taste and adjust seasoning.
Ladle into bowls and top with Parmesan, if using.
Video
Notes
Note 1: Measure 1 teaspoon fennel seed into a plastic bag, then crush with a meat mallet or the bottom of a frying pan until powdery. A nut grinder also works.Note 2: Use good-quality refrigerated tortellini (not frozen). Rana’s 5-Cheese is my favorite.Storage: Use a wire skimmer to remove tortellini and store separately from the broth. Keep both in airtight containers in the fridge for 3–4 days. Reheat broth first, then stir in tortellini just before serving to prevent bloating.