This soup’s bright green color is enhanced by the addition of uncooked spinach at the end of cooking. The tartly contrasting yuzu custard (not shown) adds a sharp yet creamy tanginess to the finish. Yuzu juice is available in Asian specialty markets in bottled form. It’s sometimes possible to find fresh yuzu citrus, but only in a domestic variety from California; Japanese Yuzu can only be imported from Japan in bottled form.
For the asparagus soup:
2 tablespoons butter or extra-virgin olive oil
1 ½ cups finely chopped yellow onion
Pinch finely ground salt
1 large potato, peeled and diced
1 bay leaf
6 cups chicken stock
Salt and freshly ground black pepper
2 pounds asparagus, tough ends removed, chopped
2 teaspoons finely chopped fresh thyme leaves
2 cups tightly packed fresh spinach leaves
1 cup heavy cream, chilled
juice and freshly grated zest of 1 lemon
For the yuzu custard:
2 egg yolks
3 tablespoons sake
Finely ground salt and freshly ground black pepper
2 tablespoons Yuzu juice (See Chef’s Note)
¼ cup heavy cream, whipped to soft peaks
For the soup:
Heat the butter or olive oil in a large saucepan over high heat. Add the onions and stir to coat. Lower the heat and add a pinch of salt. Cook, stirring occasionally, until the onions are soft and translucent, about 10 minutes, but do not brown. Add the potato, bay leaf and chicken stock. Bring to a boil, then lower the heat to a simmer. Adjust the seasoning with salt and pepper, if necessary. Cook until the potatoes are tender, about 10 minutes. Add the chopped asparagus and thyme. Return the stock to a simmer. Cook until the asparagus is just tender.
Remove the bay leaf, and strain away about half of the cooking liquid, reserving. Add the spinach to the remaining soup, and quickly purée using an immersion blender. Purée until the soup is totally smooth, with no shreds of spinach remaining. You may add back cooking liquid a little at a time until the soup reaches the desired consistency. You may also use a blender, working in batches, blending until the soup reaches an even consistency. Add the cream, lemon juice and zest, and season with salt and pepper.
[Chef’s Note: If you plan on making the soup a day ahead of service, you should quickly cool it using an ice bath, and to help retain the fresh green color, add a spoonful of powdered ascorbic acid, or vitamin C when puréeing. The quicker you cool it, the more it will keep its green color.]
To make the yuzu custard:
Bring 2 inches of water to a simmer in a large saucepan. In a non-reactive bowl large enough to rest in the saucepan, whisk together the egg yolks and sake. Season lightly with salt and pepper. Set the bowl inside the saucepan but not touching the water, and whisk constantly, adding yuzu juice little by little until the mixture has thickened to point where the whisk can leave a clean trail on the bottom of the bowl, about 3 to 5 minutes. Remove the bowl from the heat. Whisk vigorously for 1 minute to cool and thicken a little. Add 1/3 of the whipped cream. Whisk until smooth and then fold in the remaining whipped cream, being careful to keep the mixture light and airy.
To serve, warm the soup over medium heat. Ladle into warmed bowls. Use 2 medium spoons to form quenelles of the yuzu custard and garnish each bowl of soup with one spoonful.
Photo by Mary Luz Mejia