So, what I'm leading to is that if you're making soups with little in them, then you may find it a struggle to make them delicious. However, when I first arrived in London and was cooking at a restaurant called Frith's, in Soho, run by a colourful Italian woman called Carla Tomasi, she once served me an incredible broth made from just water, rosemary leaves, the most delicious extra virgin olive oil, and salt. I realised then that flavour can be produced in unexpected ways, and was really blown away by the simple, subtle taste.
In many ways, the chicken broths of Chinatowns around the world are also incredibly simple, starting with an old boiler, some ginger, spring onions, rice wine and a little seasoning and water. When I was taught to make chicken stock at college it involved huge amounts of diced vegetables and herbs, wine and fuss. I tend to steer towards the more simple Chinese style at home, and the more complex at work.
In the same way that I make my stock for risotto in the actual rice itself, that is how I make soups. I just don't see the point of making a vegetable broth in order to flavour a vegetable soup. Unless you want to make a thin broth (which is really another name for stock) then why not make a good chunky soup as you make the stock?
Caramelise, in butter or olive oil, sliced onions, leeks, garlic, ginger, lemongrass, chillies, spices, hard herbs, however many you want or need. This caramelisation adds a huge amount of body and flavour to a soup. Sometimes I cook butter to a nut-brown colour before sautéing the ingredients in it as it also adds a layer of flavour. Next, add your chopped up veges. If you're using pumpkin, kumara or root vegetables, roast chunks until golden in the oven beforehand to add some umami. Next add water, salt (some soy or miso paste works well here) and bring to a boil. Turn to a simmer and put the lid on then cook until done - the lid keeps some flavour in. You can keep it chunky or blitz with a stick blender and check for seasoning. A dollop of pesto (containing umami-rich parmesan) or similar can really make a soup fabulous too.