First, cook the noodles, then drain them, rinse in hot water, and set them aside.
Make the broth. Bring the stock to a simmer in a large saucepan. Add in the miso paste and the tahini and whisk together, then add the fish sauce. Let this simmer gently while you prep everything else.
Prepare the inclusions, starting with the mushrooms. Dice them, then sauté with butter and olive oil, stirring occasionally, until they are golden brown. Move the pan off heat and save. (You may also do this ahead of time and reserve the mushrooms, covered, in the fridge.)
Cut the greens into bite-sized slices. Slice the scallions into little coins.
Prepare the protein. We used a leftover pork chop from last week's Korean Style Pork Chop recipe, slicing the meat very thin. Instead, you could use tofu cubes (sautéed or not) or thinly sliced cooked chicken or even braised beef. If your protein requires cooking, you can also do this ahead.
Assemble the soup. Using tongs, divide the noodles between two large bowls; you may not use all the noodles. Turn up the heat under the stock so it begins to boil. In each soup bowl, artfully arrange a big spoonful of the cooked mushrooms, a fan of the protein and a little pile of greens. Finally, gently ladle the hot broth over everything—it will heat everything nicely and your arrangement won't be disturbed. That's it. The best utensils for this are a big soup spoon and a pair of chopsticks. Oh, and if you are messy like us, great big napkins.