Heat oil and butter in a large skillet (or in your 6QT or larger Crockpot™ slow cooker if it has a saute setting). Add leek and salt and cook until softened. Add garlic and cook 2 minutes more, stirring frequently.
Transfer this mixture to your Crockpot™ slow cooker if done separately. Add broth and pepper; cook on low setting for 6-8 hours, or high for 3-4.
Add tortellini, cream and asparagus. Cover and cook 45 minutes more on high setting. Stir in kale/spinach and cook until just wilted. Top with chili flakes and more parsley to serve.
Notes
*You may substitute 1 large onion and 2 stalks of celery for the leeks.