Melt butter in a large saucepan over medium heat. Add onion and saute until translucent.
Add tomatoes and their juice, salt, pepper, baking soda and thyme. Bring to a boil, reduce heat and simmer uncovered about 15 minutes or until slightly thickened.
Using an immersion blender, process until smooth. Alternatively, transfer contents to a blender and process until smooth.
With soup over low heat, slowly stir in orange juice and heavy cream. Season to taste with salt and pepper.