This soup is equally good served hot or cold.
Saute onion in butter. Add zucchini, bouillon cube, and water, and bring to boil. Simmer until vegetables are soft – about 10 minutes. Season with salt and basil. Put in blender and whirl until smooth. Add powdered milk and mix well. (Or, cook vegetables in less water and make up the difference with whole milk; milk, however, should not be boiled.)