My soup was horrible.

As Teetime pointed,could be the onion has tainted it if its overcooked.

Leek and potato can be quite bland. I always sling in some dried, mixed herbs and don't forget a bit of salt.
My favourite soup is vegetable, with whatever veg you have, even frozen, a chicken or beef stock cube, herbs, and even put in pearl barley or lentils if I have them. It often tastes better the day after!

Tastes unpleasant in what way gpip?

Did you simmer the vegetables too long?

I always add an appreciable quantity of cream to soup.

As well as improving the flavour, you get the added frisson of adding an ingredient that the food police disapprove of.

Too much green from the leek can make food very bitter. I suspect that was the culprit. I make soup with whatever I have at hand. Sometimes I make special soup with sweetcorn!

A tablespoon of ginger wine is a good addition to leek and potato soup (vegan society recipe)

Stir in a spoonful of curry paste. That should make it palatable!

I make leek and potato soup regularly and find it differs greatly each time, especially if I use a different stock to the one I'm used to. I can only suggest adding pepper and more onions/lleeks to give it a bit more flavour. But I like the idea of adding a packet of soup - although that may go against the grain, I guess.

I think Elegran may have cracked the mystery. Never done that myself but I just googled.

if my home made soup is a bit tasteless, I add a packet of soup to it (appropriate flavour obviously!) and loads of seasoning, and that seems to do the trick.

I always use Knorr Stock Pots for soups, they are more flavoursome. They are quite salty so watch your seasoning.
Good luck with the next batch.

Did you over-blitz it? If there were potatoes in it, that would turn it into a wallpaper paste consistency. Yukky.

Are your stock cubes the lower salt variety? I sometimes have to add another one, or half a cube to my soup to get more flavour.

I have stopped putting onions or garlic in soups and stews as they give me heartburn.
I use the tip of a teaspoon of asafoetida instead, to give the savoury onion flavour.

Red lentils which don’t need rinsing, with potatoes, carrots parsnips tin of chopped toms, oxo cube, anything else on the turn into a large pot.add water.
Cook and stir to stop burning for about half hour/4o mins til the potato, parsnip and lentils thicken it all. Add anything else you want. Voila! Always works. Easy to freeze or eat with crusty bread. Enjoy.

My firm favourite is just tomatoes and onions roasted in the oven with garlic, a little balsamic, pepper and olive oil. In the soup maker with lots of basil and stock (I like Marigold). Delicious, but sadly the tomato glut’s well behind us now.

Peppers instead of tomatoes make another lovely summer soup.

It does sound like a stock failure if it’s your usual recipe.

I make loads of soup from the allotment surplus and whatever’s in the fridge. I’ve been known to throw a few olives in or half a jar of pesto if they need using.

It mainly ends up in the freezer and occasionally it turns out to be a real triumph. Shame I can never repeat it as I can’t remember what I put in that stuff I labelled “green soup”.

I don't know why your soup failed. Could be the stock cubes (easily tested, bung one in a cup of boiling water and smell & taste), but I have had horrible spuds at a friend's. She'd kept the raw spuds in the fridge and that alters the taste and starch structure. Also leeks that aren't cooked enough can be a bit unpleasant.

I would guess that there is something wrong with the stock cube. Tainted in some way. Bin it and start again. Check out the pack too.

If you've always made soup, I'm not sure I understand why you're now asking for recipes after just one failed batch?

I always make soup, usually, like Teetime, using whatever veg is to hand. Occasionally (rarely) I have a poor result, but put that down to experience and move on. One of my favourites is lentil soup, made with green or brown lentils, often with bacon pieces.

Onion, carrot star anise.

I do whatever vegetables are at hand for my soup. sweat off an onion ( careful not to burn or it will taint the soup) then add the chopped hard veg (carrots, squash) then when they are softened add chopped leeks, celery and potato if not using pearl barley or other grains. I throw in some herbs, coriander sometimes fennel seeds or cumin then vegetable or chicken stock. Season well after blitzing with the stick blender , throw in any left over chicken if there is any. Tastes different every time depending on veg used.