Heat olive oil in a large pot over medium heat. Add onion and cook 6–8 minutes until translucent and beginning to brown.
Add garlic and cook 30 seconds until fragrant. Push onions to the side.
Add sausage to the pot; brown thoroughly (5–8 minutes). Break up if using crumbled sausage. Remove excess fat if desired (leave some for flavor).
Add cauliflower; stir to combine. Pour in chicken broth, scraping up any browned bits. Bring to a gentle boil, reduce to simmer, and cook 8–12 minutes until cauliflower is tender.
Stir in kale; cook 2–3 minutes until wilted.
Reduce heat to low; stir in heavy cream and Italian seasoning. Warm through (do not boil). Taste and adjust salt/pepper.
Serve hot, garnish with Parmesan and red pepper flakes if desired.