Melt the butter in a medium saucepan and gently sauté the onions until tender, approximately 3 to 5 minutes. Add the cream cheese, stirring while it melts. Do not let it burn. Mix in the tomato soup until smooth. Turn off the heat. Add the milk slowly, mixing well. Return to heat to continue cooking. Add the diced tomatoes and basil. Stir and heat until hot. Add parsley or sprinkle parsley on top of each bowl when serving. For a thicker soup, add cooked wild rice.