Heat oil and butter in a skillet. Saute onions and clams, adding the garlic powder, oregano, salt, pepper, and cayenne. Cook onions until tender.
Add the flour and mix well, heating the flour for about 30 seconds to get rid of its taste. Pour in chicken broth, clam juice, and cream. Bring to a simmer and add Parmesan cheese. Simmer and stir until cheese is melted.
Served over cooked pasta. (Make sure to salt the cooking water for the pasta well.)