onion puree thickness From times to times, I make this soup that consists of 90% onions and 10% green pepper/garlic/white cabbage/carrots. Not matter how much water I add to it, it always ends up quite thick after blending. I own 2 different (Though not particularly priced) hand blenders and normally try to blend the onion stock with both and sieve it, however after blending the soup, there is a thick layer with a paste-like consistency in the sieve that no matter how much I try to scrape using a soup, it just won't strain through. Could I be undercooking the stock? 

My method is normally: 1.5kg - 2kg of onions, 1 green pepper, 2 carrots, 1 piece of cabage same weight as carrots. I put it all in the pressure cooker and boil it for about 20 - 40 mins after it peaks pressure in a low heat. On another note, I also notice this puree/stock/soup never really gets very sweet as I would hope it to. Perhaps I need to simmer it longer so as to help the onion and other veg to break?

Thanks.
For starters, the pasty stuff in your sieve is most likely just fiber from the vegetables. Cabbage and carrots in particular have a lot of fiber and unless you have a really high powered blender, you're not going to break it down enough to pass through a sieve. Most immersion blenders certainly won't be able to do it.

As for the sweetness, usually to bring out the sweetness in vegetables, they are roasted before the liquid is added to make the base of the soup. You could try roasting the carrots and peppers or caramelizing the onions as a prior step.