Soup Series: 1, my spinach and sorrel soup

I'm going to be doing something special in the next few weeks on this blog, to celebrate the cosy joys of winter cooking: a series all about soup, with guest posts by fellow authors presenting their personal favourites.
This one's the introductory post, by me, and as it's appearing on the day of the official launch of my latest novel, Scarlet in the Snow, which has its inspiration in Russian fairytale, I'm presenting a soup of my own invention, but with a Russian flavour, a soup that Sveta, the family cook in Scarlet in the Snow, could well have cooked for my heroine Natasha and her mother and two sisters, Liza and Anya. I've featured this soup before on the blog, but I think it deserves another outing!

Spinach and Sorrel Soup

Spinach and sorrel are two leafy greens that keep going in our New England winter, even if they're not in the same wild profusion as in spring. If you can't get sorrel, you can add instead a squeeze of lemon juice to spinach and chives soup.
Finely slice a couple of potatoes and half an onion. Sauté in some butter, with some crushed garlic. Add the washed spinach and sorrel(much more spinach than sorrel--only a small handful of sorrel will do.) Stir around. Add chopped garlic chives and parsley. Add a splash of white wine, then good stock--chicken or good vegetable stock. Add pepper, salt if needed(check, though, as stock is often salty). Bring to a boil then simmer for about 25 minutes. Take off the heat and either mash the vegetables with a potato masher, as I did, or whizz in a blender. In a bowl, mix one egg yolk and about three tablespoons milk, stir, and then add to the hot soup. Serve with chives or any other herb you want.
Simple and very tasty! I recommend making it a few hours before you eat it as then the flavours have time to develop.