The ingredients in potato soup are potatoes, a liquid base, like milk, broth and cream, aromatics like onion, garlic, celery and carrots, thickeners like butter and flour, seasonings like salt, pepper and herbs.
Some popular toppings for potato soup are green onions, cheese and bacon which makes for a nice creamy hearty potato soup.
The potatoes that are commonly used in potato soup are russet potatoes, although you can use other potatoes if you prefer.
You can even make sweet potato soup, by sweet potatoes instead of regular potatoes.
I've tried this before when I ran out of regular potatoes and the sweet potatoes made for a nice sweet potato soup.
Some common mistakes to make when making potato soup are using the wrong potatoes like waxy potatoes vs starchy potatoes, adding dairy too early or even using low fat versions of dairy, over blending which causes sliminess, under seasoning, or even forgetting to saute the aromatics first, which results in bland, gritty or overly thick potato soup.
To fix this issue, use starchy potatoes in your potato soup, like Russet potatoes, add dairy like heavy cream/half and half at the end of cooking on low heat, blend it minimally and build flavor in your potato soup with quality stock and sauted onions and garlic.
Using waxy potatoes such as red potatoes results in firmer chunks in your potato soup, and using starchy potatoes like Russet potatoes break down creamier textures.
Russet potatoes can also get gritty though if they are over blended.
Using a blender or food processor blending the potatoes for potato soup can also burst starch cells and make the potato soup gluey and pasty, so using a potato masher, ricer or immersion blender, partially is better.
Also adding too much liquid to your potato soup is also a common mistake as potatoes absorb flavor, so don't drown the potatoes, you can also always add more liquid later if needed.
Another common issue is over salting the potato soup, especially with pre-made broth.
You can fix this issue by simmering an extra unseasoned potato to absorb the salt, then remove or dilute with some broth or water.
High heat can also curdle milk or cream and cause lumps, so add any dairy after removing from heat or on very low
Using low fat milk instead of cream or half and half also results in thinner and less rich potato soup.
And boiling the potato soup too aggressively can also make the potatoes grainy or cause the dairy to curdle.