In a med. pan melt butter over med. heat. Add onion and garlic (my kids hate onions so I sneak onion powder in instead and I use less garlic this is alittle too much for me). Cook until onion is soft, approximately 15 minutes, stirring occasionally. Add tomatoes, stirring to combine. Simmer for 10 minutes.
In a small bowl, combine flour and chicken broth, whisking well. Slowly add to tomato mixture, stirring well. Cook for 10 minutes.
Pour mixture into the work bowl of a food processor and pulse until mixture is smooth. Return tomato mixture to a saucepan. Add half-and-half, stirring to combine. Cook until heated through, approximately 10 minutes.