Heat butter in a Dutch oven over medium high heat. Once the butter is melted, add onions and garlic and sauté until onions are translucent, about 3 minutes. Meanwhile, puree tomatoes in a blender.

Add pureed tomatoes, clam juice, parsley and dill to the Dutch oven. Bring to a simmer. Add salt, pepper and salmon. Gently stir to combine. Simmer until the salmon is fully cooked, about 5 minutes.

Meanwhile mix the flour and heavy cream in a small bowl. Whisk until the flour is well combined in the cream.

Slowly add cream to the soup, once the salmon is cooked. Simmer until soup has thickened slightly, about 5 minutes.

Serve hot.