Begin by heating a large frying pan over medium-high heat. Crumble the Italian sausage and add it along with the diced onion, cooking for about 4-5 minutes until the sausage is browned and the onion becomes translucent.

Stir in the minced garlic to the sausage mixture and let it cook for an additional minute, until fragrant and slightly golden.

Carefully transfer the fragrant sausage and onion mixture into your slow cooker.

Add the chicken broth, cubed potatoes, salt, pepper, and red pepper flakes to the slow cooker, stirring well to combine all ingredients.

Cover the slow cooker with its lid and set it to low for 4-5 hours or high for 2 hours.

In the last 30 minutes of cooking, gently stir in the chopped kale, heavy cream, and grated Parmesan cheese into the soup.

Once ready, ladle the comforting soup into bowls and serve warm.