Melt butter in a deep frying pan over medium-high heat. Saute onion and celery until tender, 3 to 5 minutes. Add milk, canned soup, potatoes, dill, red chilli flakes, black pepper, caraway seeds, hot pepper sauce and salt. Bring to a boil. Simmer until potatoes are slightly tender, about 15 minutes. Add salmon and shrimp. Cook until opaque, about 3 minutes.
You can replace celery soup with 3 tablespoons powdered soup and increase milk by 1 cup.