I am famous for my soup, but don't think I have a 'secret' as such, just make it the way my Dad did, as taught to him by his Mother. He used to say that you needed good stock and at least 10 different ingredients to get a depth of flavour. I suspect tho' that your soup Jeni suffers from being made in small quantities. Here I make a huge pot 8-10 servings. It lasts for 3-4 days with a boil up each day and the taste and texture improves each day. My occasional attempts at specific, eg Parsnip, Lentil soups, from a recipe in small quantities are never very successful tho' I do make a mean French Onion as follows:
In a saucepan, saute two finely chopped, large onions and one stick of celery - very finely chopped in a little butter or olive oil until beginning to brown. Add two pints of veggie stock, french herbs, paprika, a splash of SOY SAUCE, 2 splashes of RED WINE, SHERRY OR PORT. Simmer for an hour or more, serve with french bread or cheese floats if liked.