Wild Mushroom, Walnut and Tarragon Soup

It’s the time of year again for wild mushrooms and as you’ll see I’ve been cooking with them quite a bit lately. I’d like to say I went out and picked them all myself but I haven’t because I still don’t know enough to do so with any confidence. Although there aren’t actually many fungi that will kill you it’s still a risky business and not something I’m going to take any chances with so for this soup I bought them in Fallon & Byrne (funnily enough I haven’t seen many in the farmers market this year). I also used some portobellos to bulk it out as they’re much cheaper.

Various wild mushrooms

There are two unconventional stages in this recipe, the first is rather than using cream I made my own walnut milk which is actually very easy. Just whizz the nuts in a blender with some warm water for around two minutes and then squeeze the ‘milk’ out of the resulting pulp. Now, I’m obsessive about getting the smoothest texture for soups and sauces so when I heard about these things called Suberbags they use in El Bulli for straining almond milk I decided to investigate a bit because the gritty remnants of that pulp floating in my bowl does not appeal very much.

It turns out some enterprising company is selling standard industrial filters to chefs for €50 a pop. You can get them in 100, 400 and 800 micron (μm) sizes but I managed to find functional equivalents from an English website selling equipment for the production of biodiesel! I even got one with a finer mesh size of 50μm as well as 100μm and the two still cost less than one Superbag. The only downside is the shape is a bit awkward but I still use them for everything from straining stock to making elderberry syrup. Obviously, I know not many people are going to have these filters so the instructions below detail how get a similar effect using cheesecloth (beware though, some of the pulp will leak out).

Walnut milk

The second unusual step is that I use egg as a thickening agent: this is a very old-fashioned technique but gives a lovely mouthfeel to the finished product. A liaison would normally be made with the yolks and double cream but here I’ve omitted the latter. You have to be very careful to avoid curdling so tempering by mixing some soup into the beaten yolks before pouring that mixture to the pot is vital. Then you have to stir constantly and ensure it doesn’t reach the boil (or even close, anything over 80°C will cause clumping). I normally aim for keeping the liquid under 75°C just to be safe.

Mushroom, Walnut & Tarragon Soup

Serves: 4

Ingredients:

200g walnuts
150g wild mushrooms, roughly chopped
250g Portobello mushrooms, roughly chopped
Salt
Grapeseed oil
50g butter
100g onions, finely sliced
2 large cloves garlic, roughly chopped
10g tarragon, chopped
50g celery, roughly chopped
50ml pernod
800ml veal stock
Worcestershire sauce, splash
5g pepper
1 bay leaf
1 parmesan rind
3 egg yolks
2.5ml sherry vinegar

Method:

  1. Soak the walnuts in cold water overnight.
  2. Drain the nuts and put in a blender or food processor with around 250ml of warm water.
  3. Blend for 2-3 minutes.
  4. Pour the resulting paste into a sieve lined with cheesecloth and tie the cloth to seal the top.
  5. Squeeze as much of the liquid as you can out of the paste and collect in a bowl.
  6. Place a large pan over a high heat and add the mushrooms and enough water to stop them catching and burning.
  7. Add some salt and cook the mushrooms down until they’ve collapsed a bit and released their moisture. (Around 5-6 minutes.)
  8. Strain the mushrooms from the pan into a sieve and squeeze out as much water from them as you can. Reserve the liquid.
  9. Wipe the pan clean and return to the high heat and add some grapeseed oil.
  10. Add the mushrooms (in batches if necessary) and fry for a couple of minutes until slightly golden on the edges, being careful not to over-colour them.
  11. Remove from the heat and reserve.
  12. Melt 15g of butter over a medium heat and when foaming add the onions and sauté for around ten minutes until softened.
  13. Add the garlic, celery and tarragon and cook for another five minutes.
  14. Pour in the pernod and boil off the alcohol.
  15. Add the stock, walnut milk, reserved mushroom water, bay leaf, Worcestershire sauce, pepper and parmesan rind.
  16. Simmer for around twenty five minutes.
  17. Remove the bay leaf and parmesan rind and transfer the liquid to a blender.
  18. Blend until smooth and pass through a fine mesh sieve into a clean pot over a low heat.
  19. Beat the egg yolks with a whisk and then whisk in a ladle of the soup.
  20. Pour the egg mixture back into the pot and stir continuously. Do not allow the soup to approach anything like a boil or the eggs will curdle.
  21. Cook for around five minutes, stirring the whole time and ensuring the soup stays below 75°C
  22. Stir in the sherry vinegar and the rest of the butter and adjust the seasoning if required before dividing between four bowls to serve.

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