Put slightly more than 6 1/5 cups (1.5 L) of water to boil on the stove and put the diced potatoes and zucchini in it. Add a little salt. Drain and blend the ready vegetables.
Add the milk and mix together with 2-3 cups of the vegetable broth. Add the corn and butter and put to boil until the corn softens.
Season the ready soup with salt and pepper. Serve sprinkled with feta cheese and parsley.