Make a stiff dough with the flour and water. It should be a little stiffer than noodle dough. If the dough is too soft, the mashi will fall apart or lose their shape when boiled.
After kneading for several minutes, let the dough rest. Cover the dough with a bowl and let it rest about 30 minutes.
After resting, the dough should be smooth and glossy.
Mashi are traditionally rolled on baskets to create texture. Use a basket, fork, or cavatelli/gnocchi board as your rolling surface.
Take a marble-sized piece of dough. Use your thumb to roll it across the board. This will create a lined pattern. You can roll along, against, or diagonally across the line of board to create stripes.
To make the soup, start by heating the oil in a wok. Add the garlic, ginger, leeks, and Sichuan peppercorns. When fragrant, add the hearty vegetables like cauliflower, potatoes, tomatoes, and shitake mushrooms.
After stir-frying the vegetables, use a soup pot to boil the mashi. Boil the mashi in a large pot of water for about 10 minutes. The boiling water will become the liquid for the soup, so use the amount of water that creates the amount of soup you would like.
Once the mashi are finished boiling, ladle the stir-fried vegetables into the pot of mashi and water.
Add handfuls of raw bok choy, soybean sprouts, and woodear mushrooms to quickly blanch into the soup. Because the liquid of the soup is the cooking water from the mashi, the soup is a little thick and starchy, which is supposed to be good for digestion.
Once all of the vegetables are combined with the mashi soup, add splashes of soy sauce and black vinegar. Adjust for salt.
Ladle into bowls. Serve with black vinegar and chili sauce on the table.