Heat olive oil in a skillet and cook the sausage until browned. Break it into pieces as it cooks.
Add the chopped onion and garlic, cooking until fragrant and soft.
Transfer everything into a slow cooker. Add potatoes, chicken broth, and crushed red pepper flakes.
Cover and cook on low for 5-6 hours, until the potatoes are tender and the flavors have mingled.
Stir in half and half and kale. Cook for another 15–20 minutes until the kale softens.
Season with salt and black pepper, give it one final stir, and serve hot with a slice of crusty bread.