Broth

• 7 cups dashi (basic sea stock)
• 1 teaspoon salt
• 2 tablespoons usukuchi shōyu (light soy sauce)
• 2 tablespoons regular soy sauce
• 3 tablespoons mirin (syrupy rice wine)
• 1 tablespoon sugar
• 1 small onion, peeled and cut in half
• 1 package (5 grams) OR about ⅓ cup katsuo bushi (dried bonito flakes)

Noodles

• 12–14 ounces fresh, uncooked udon (thick white noodles) OR 8–10 ounces dried udon (flat white noodles)

Toppings

• 4 jumbo shrimp
• 1 tablespoon saké (Japanese rice wine)
• 1 tablespoon cornstarch
• 2 ounces fresh spinach, with leaves still attached to stems (You’ll need two 6-inch lengths of kitchen twine to tie the spinach, too)
• ½ teaspoon salt in 2 quarts boiling water
• 4 large whole eggs
• 2 packages enokidaké (slender creamy-white mushrooms), 3½ ounces each

In a 3- or 4-quart saucepan, season the stock with the salt, light and regular soy sauces, syrupy rice wine, and sugar. Stirring occasionally, heat through until the salt and sugar have dissolved. Add the onion and simmer for 5 minutes over medium heat. Remove the pot from the heat, sprinkle the bonito flakes over the soup, and let it stand for 2 minutes. Pour the soup through a cloth- or paper-lined strainer or colander, discarding the solids.

Bring 6 or more quarts of water to a rolling boil in a large stock pot. If you’ve been lucky enough to find fresh udon noodles, add them and cook for 8 minutes after the water returns to a boil or until each noodle is barely tender: firm but with no hard core at the center. The noodles will be briefly cooked again later. Drain and rinse the noodles under cold water and drain again.

If you’re using dried noodles, cook them in a very large pot in at least 6 quarts of boiling water until the water returns to a boil. Add 2 cups of cold water and wait for the water to return to a boil a second time. Now cook the noodles for 7–8 more minutes in water that’s kept at a constant boil. Test a strand; it should be firmer than the Italian al dente since the noodles will later be cooked again, but not so raw as to have a hard core remaining at the center now. Drain the cooked noodles, rinse, and drain again. Set the cooked noodles aside until all the toppings have been readied.

Peel and devein the shrimp. Stir the rice wine and cornstarch until well combined, in a small dish just large enough to hold the shrimp. Add the shrimp and marinate them in the wine and cornstarch mixture for 3–4 minutes while bringing several cups of water to a rolling boil in a small pot. Add the shrimp to the boiling water, stir, and wait 1 minute before straining them through a small colander or strainer. Set aside while you finish making the other toppings.

Rinse the spinach and shake dry. Divide the spinach into two bundles and tie the stems of each with kitchen twine. In a wide-mouthed, shallow pot bring about 2 quarts of water to a boil. Add ½ teaspoon salt and quickly plunge the spinach stems first into the salted water. Stir if necessary to wilt all the leaves and stems, then drain the spinach immediately, refreshing it under cold water. Squeeze the spinach dry, and trim off and discard the very bottoms of the stems with the twine. Slice the spinach into 1-inch lengths and divide into four portions before setting aside.

Break each of the four eggs into its own small bowl, being careful not to puncture the yolks. Cover the eggs and set aside.

Rinse the enokidaké mushrooms under cold water and trim off the bottom halves of the stems. Pat the mushrooms dry and divide into four portions.

The Japanese use individual heat-proof casseroles with lids to finish cooking and serving this soup. If you have them, or any 3- to 4-cup capacity containers with lids that can withstand direct heat, follow the procedure described here: Divide the broth among the four containers. Place them on the burners and heat the broth just to a gentle boil. Add the noodles and simmer for 30 seconds, skimming the surface if necessary to remove any excess starch coming from the noodles. Allow the soup to return to a gentle boil, then pour one egg into each casserole and cover. Simmer over medium-low heat. The Japanese like the whites firm but the yolks rather runny; that happens after approximately 3 minutes of poaching. Most Americans prefer a firmer egg, which will take about 2 additional minutes of poaching. Remove the cover from each of the casseroles and, without hiding the egg from view, lay a shrimp, then a portion of mushrooms and a bundle of spinach next to each other and over the noodles and bubbling broth. Replace the covers, then remove the casseroles from the burners and serve at once.

If you don’t have individual cooking casseroles, you’ll need to poach the eggs separately before assembling the soup. Heat through the seasoned broth and add the cooked noodles. Just as the soup reaches a boil, remove it from the stove. Immediately divide the soup and noodles among four deep soup bowls. Place a poached egg and blanched shrimp on top of the noodles in each bowl, then add some mushrooms and spinach to each serving, gently submerging these last two beneath the piping-hot soup. Serve at once.

Since this soup would be difficult and messy to serve at the table from a large communal pot, I don’t recommend making this dish in a single large casserole. Rather, you might take advantage of a microwave oven to heat preassembled individual bowls of soup with their toppings. In that case, divide the cooked noodles among four deep soup bowls. Gently lay a poached egg, a blanched shrimp, a portion of mushrooms, and a bundle of spinach over each bowl of noodles. Pour the seasoned broth over all, being careful not to break the yolk. Cover each bowl with clear plastic wrap and place in a microwave. Set the oven for “boil” for 15 seconds. Remove the plastic wrap and serve at once.