Place your chopped vegetable(s) and onion into enough broth or stock to cover them and boil until soft.
Pour everything into a blender and process until smooth. (Strain, if necessary.)
Return to saucepan. Stir in just enough milk to reach desired consistency. (Be very careful when adding milk, so that you do not use too much. Excessive milk will kill that great vegetable flavor.) Heat through, but do not boil so that milk will not curdle.
Serve in bowls with a small pat of butter in each.
If you'd prefer your soup slightly "chunky," blend only 3/4 of the cooked veggies with the soup stock. Add the reserved veggies back in together with the milk.
Basic Cream of Any-Veg Soup https://comboplate.net/basic-cream-of-vegetable-soup/