1. Cook pasta according to package directions in well-salted water. The water should be salty like the ocean. Reserve 2 cups of pasta water before you drain it.
2. While the pasta is cooking, heat olive oil in a large, deep pot over medium high heat. Add the celery and onion. Saute until tender – about 10 minutes.
3. Add the sausage. Cook, breaking into small pieces, until browned all the way through.
4. Turn the heat down. Add the garlic, and tomato paste. Sauté until fragrant and the tomato paste has turned from bright red to a deep red/brown – about 3 minutes.
5. Add the chicken stock & heavy cream; let it come to a simmer. Stir in the kale. Season with salt and cook until the kale is wilted.
6. Toss the cooked pasta in the sauce. Add the reserved pasta water as needed to thin the sauce.
7. Top with red pepper flakes and freshly grated parmesan cheese.