In a large pot, cook the sausage over medium-high heat for 4 minutes using a spatula to break up the meat. Add the onion and cook for 5 to 6 minutes- until the onion has softened and the sausage is cooked through.
Tilt the pan and spoon out and discard any grease that has accumulated in the pan. Add the garlic and continue to cook for 1 minute. Stir in the flour and cook for 1 to 2 minutes, stirring continuously. Stir in basil, hot sauce, mustard powder, oregano, pepper and cayenne (if using). Add the chicken broth in small amounts and use a rubber spatula to deglaze the pot. Stir in the cream, bring to a boil and then reduce to simmer.
Add the tortellini, and simmer for 3 minutes. Add the kale, and continue to simmer until the tortellini is cooked through (2 to 5 minutes).
Taste the soup, and season with salt as needed. Transfer to individual serving bowls, and top with a pinch of red pepper flakes.