It's taken me thirty years but I've finally discovered it. Please ignore this if you were quicker on the button.
The secret to good soup is:
onion + potato + knorr vegetable stock cube
+ whatever else you want to put in the soup - extremely simple seems to work best
= delicious soup! Every time!
If you'd like more detail...
Chop and gently fry an onion. When it's soft add your potato, as much as seems reasonable. In a little bit, add the stock you've made with your stock cube/s, (I think the other flavours don't work half as well as vegetable), and put in the other vegetables when it makes sense. So, today, I rescued some dying artichokes from the bottom of the fridge and put them in with the potatoes. Last week, it was broccoli, so that went in about fifteen minutes after adding the stock, and then it simmered gently - (i hear that if you boil things too hard you kill all the nutrients and flavour - I'm told the issue is all about temperature much more than time) - for about five minutes more, then wizz it up and add salt and pepper (at any stage I think) and you're done.
O, a hand blender. That's the fourth magic ingredient.
onion + potato + knorr vegetable stock cube/s + hand blender = delicious soup from any old veg you've got.
2 years ago