In a large pot, sauté the onion in 4 tablespoons of the butter, and add the salt and oregano until translucent, about 4 minutes.

Add in the chopped tomatoes and chicken broth and bring to a simmer.

While the tomatoes and broth come to a simmer, prepare a roux in a separate small saucepan. Melt the remaining 2 tablespoons of butter, then add the flour. Stirring for a few minutes until the flour just starts to brown.

Add the cream and half-and-half, stirring constantly until just simmering. With the heat on low, cook the mixture for 20 minutes, covered. Add the mixture into the pot with the tomatoes.

Purée the soup with an immersion blender.

Season to taste with salt and freshly ground pepper, and serve.

If the tomato soup ends up separating, just re-blend it with your immersion blender.