Persian-Inspired Noodle Soup (based on Ash Reshteh)

I've played fast and loose with this recipe, I think, substituting all sorts of things for other things, so that I'm using things from my own backyard. The herb mix in particular honours the Persian use of lots of herbs, but the herbs I use are my own blend, and while I use nasturtium leaves for that almost floral note they bring, I recognize that it is a more rare ingredient to have on had, and spinach makes a fine substitution and is closer to the original anyway.

2 Tbsps. olive oil

1 onion (6oz/170g) thinly sliced

1 long red chili OR green serrano chile, finely chopped

1/2 tsp turmeric

1 tsp ground cumin

1/4 tsp freshly ground black pepper

100g/3.5oz French lentils, green lentils, yellow split peas or brown lentils

8 1/2 cups vegetable stock/broth or water

400g/14oz cooked chickpeas

350g cooked cranberry beans or borlotti beans

2 tsps. salt, to taste

120 g thin egg noodles, linguine, or spaghetti, fresh or dried

3 1/2 oz/100g nasturtium leaves (or spinach, trimmed) finely shredded

⅓ cup (20g) parsley, finely chopped

2 Tbsps. (8g) fresh dill, finely chopped

1 Tbsp (2–3g) fresh tarragon, finely chopped

juice of one lime, plus more to taste

Toppings:

1 Tbsp extra virgin olive oil

1 Tbsp butter

1 large onion, thinly sliced

1/2 cup sour cream, creme fraiche, full fat yogurt or liquid kashk

50 g / scant 2 ounces of toasted, chopped walnuts

1. Heat the oil in a large, thick-bottomed soup pot over medium heat. Add the onion and the chilli and cook until they soften, 8 minutes or so. 
2. Add the spices and cook for another thirty seconds, just long enough for them to toast a bit and release their aromas, then stir in the lentils (or split peas) to toast for a couple minutes.
3. Add the broth and bring to a boil cook the lentils until they are just tender, about 25 minutes. 
4. Stir in the cooked chickpeas and cranberry (or borlotti) beans and the salt. Return to a simmer.
5. In the meantime, prepare the toppings. Heat the olive oil and butter in a large frying pan over medium heat along with a couple big pinches of salt. 
6. Cook the onion, stirring occasionally, until golden and deeply caramelized, 8 - 10+ minutes. Set aside with the sour cream and chopped walnuts.
7. A few minutes before you're ready to eat, add the noodles to the simmering soup and cook until al dente, usually about 5 minutes. 
8. Stir in the greens and the chopped herbs and the lime juice. Taste and adjust the seasoning to your liking, adding more salt if needed.
9. Serve right away, each bowl topped with a big spoonful of caramelized onions, some sour cream, and a sprinkling of walnuts.