Lightly grease the bowl of a slow cooker. Add broth, cream and garlic. Cover and cook on low for 4-6 hours.
About 30 minutes before serving, combine soft butter, flour and parsley in a small bowl. Whisk butter mixture into the slow cooker until smooth. Cover and continue cooking for another 30 minutes, or until mixture is thickened.
Stir in Parmesan cheese. Serve over cooked pasta. Garnish with additional parsley and Parmesan cheese, if desired.
Video
Notes
For every 8 ounces of cooked pasta, use about 1 1/4 cups of sauce. Store leftovers in an airtight container in the refrigerator for up to 3 days.