Step 1Bring 6 cups of water to a boil, remove from heat and cool slightly. Add the tea, konbu and ginger, and set aside to steep for 10 minutes.
Step 2Meanwhile, sauté the mushrooms in the sesame oil until golden brown, then remove from heat and hold in a warm place.
Step 3Strain the broth into a small pot. Add the udon to the broth and bring to a boil. When the noodles froth up, add a cup of cold water. When the water returns to a boil, reduce the heat to a gentle simmer until the noodles are cooked.
Step 4Divide the cooked noodles between two bowls. Briefly blanch the spinach in the hot broth, then strain. Add a few cups of broth to each bowl, then top with the mushrooms, spinach and scallions. Drizzle with soy sauce as desired and garnish with sesame seeds. Serve immediately.