1Spray 1 1/2-quart slow cooker with cooking spray. Pour marinara sauce into cooker.
2Cover; cook on Low heat setting about 2 hours or until hot.
3Stir in cheese and basil. Cover; cook on Low heat setting about 30 minutes longer or until cheese is just starting to melt. Serve with baguette slices. Dip can be kept warm on Low heat setting up to 2 hours; stir occasionally.