This is NOT a recipe but a tutorial. Think of it like a "choose your own adventure" story. You can make this soup 100 ways and it will always be delicious. Just stick to the basic formula and it will always come out good!
1: Start with a stock to build flavor
You can make this yourself or use a bought vegetable stock like Imagine if you want the soup to be parve. If you have the time to make your own stock I highly recommend it. An Instant Pot makes stock making easy, but you can do it in a regular stock pot as well if you have the time. To make the stock for this soup, I follow the general directions for stock in my Leftovers Turkey Soup recipe. You can use chicken, turkey, beef or veal bones or a mix. ( I highly recommend the combination of turkey, beef and chicken bones). Make sure to roast them first! This will deepen the flavor of the stock and the resulting soup. Don't skip it!
I like to refrigerate my stock overnight when it's done so I can easily skim the fat before making my soup.
2: Chop your vegetables
Onions and garlic should be kept separate from the other vegetables. The rest of the vegetables are negotiable. Being that this is an "Orange" vegetable soup I like to use mostly orange vegetables such as butternut squash, sweet potatoes and carrots. Other good additions are celery, parsnip, turnip, zucchini, kohlrabi, fennel.
For reference as to the amount of vegetables you need: For a 16 qt pot of soup I had two sheet pans completely full of chopped vegetables (not in a single layer).
3: Roast your vegetables
Roast all the vegetables besides the onion and garlic on a parchment lined sheet pans with some olive oil drizzled on them for 40 minutes to 1 hour at 375-400. If you are making a very large pot of soup then the vegetables may not fit in a single layer on your sheet pans. That's ok. You're not going for crispy roasted vegetables here. The point is to introduce the delicious "roasty" flavors into the soup.
Don't skip this step. The difference between a soup made with roasted vegetables and just dumping the vegetables into your stock base is huge. If you can't roast the vegetables (lets say your oven is on the fritz) then sauté them for at least half an hour in the pot after the onions have started to take on color and before adding the liquid.
4: Onions and garlic
Sauté your chopped onions and (smashed with the side of a knife) whole cloves of garlic in some oil in your soup pot until they are starting to take on color.
5: Combine all ingredients
Add the roasted vegetables to the pot along with your stock and rinsed red lentils. I used two 1 lb bags of lentils in my giant 16 qt soup pot. My stock was very concentrated so I also added water. It's best to add less water now and more later if needed as you can't take it out once it's added.
Optional add ins: (wrapped in cheesecloth or in a "soup" bag for easy removal later)
Chicken thighs, flanken meat or kolichel, marrow bones
The last time I made this soup I used 2 chicken thighs and 2 marrow bones in my 16 qt pot. I removed them and added the marrow from the bones back into the pot before pureeing the soup. It was delicious!
Let simmer for a few hours. 2 is a minimum. 3-4 is even better. Stir every so often to be sure the lentils aren't sticking to the bottom of the pot.
Now you can adjust the consistency of the soup by adding more water if needed. Adjust the seasoning with salt to taste.
Now you can decide if you want to puree the soup or not. If you do be sure to remove any bones or chicken/meat before you do. I have served this soup both ways. I sometimes even take out half and puree the rest for two different soups from the same pot.
You can shred any meat or chicken that was cooked in the soup and either mix back into the soup (after pureeing if you choose to do that) or sprinkle on top of individual bowls. ( I have done both)
This soup freezes very well.