This soup is so comforting and earthy. The technique is brilliant and the taste is amazing! The recipe involves a few different phases and different types of equipment, but for us, the trouble is totally worth it since the taste is so delicious! We freeze leftovers to make easy meals for our two-year-old daughter.
If you're using frozen homemade chicken broth, unmold a quart and warm it in a pot to thaw. De-stem the shiitakes (save the stems for broth) and trim and rinse all the mushrooms, keeping them whole.
Toss the mushrooms and salt in a large, microwave-safe bowl. Cover with a plate and microwave for a total of 12 minutes, but microwave them in 4-minute increments and stir the mushrooms in between each break. The mushrooms will release their liquid and shrink.
Insert a colander into a large glass measuring cup (2 quarts or larger). Drain the mushrooms and collect the mushroom water.
Preheat the dutch oven and vegetable oil over medium heat. Add the mushrooms when the oil is hot. Cook for a total of 8 minutes. Stir every 2-3 minutes.
Add the onion, thyme, and pepper and cook for about 2 minutes until the onions are soft.
Add the sherry and cook until evaporated.
Add the mushroom liquid and stir in the fond (browned bits of mushroom) from the bottom of the pot.
Measure out the water and the broth in the large measuring glass. Stir in the water and the broth and bring the mixture to a simmer. Bump the heat down to low and simmer for 20 minutes.
Remove the thyme sprig. Working across 2-3 batches, transfer the soup to the blender and process until smooth. Pour the first 1-2 batches into the large measuring glass. Pour the last batch, along with the previously blended batches, back into the dutch oven. Stir to combine.
If you wish to store the soup and finish the final processing separately, the soup will keep in the fridge in this state for up to 2 days. Make sure to heat the soup up to 150°F before proceeding with the next steps.
In a medium measuring glass, measure out the cream and add the yolks. Whisk to combine, then slowly mix in 2 cups of the hot soup into mixture.
Pour the cream/yolk/soup mixture into the soup pot and stir and gently cook until the soup's temperature reaches 165°F.
Mix in the lemon juice and season with salt and pepper only if needed.
Serve immediately. Garnish each serving with 1 teaspoon of cream and chopped chives.