For Homemade Noodles:Combine flour, tapioca, and sea salt in the bowl of your KitchenAid® Stand Mixer fitted with the dough hook attachment. Mix to evenly combine. Slowly drizzle in lukewarm water, scraping down the sides of the bowl as needed, until dough comes together into a shaggy dough. The dough should be fairly dry and stuff, but still come together into a loose ball. If necessary, add an additional 1-3 tablespoons of water, 1 tablespoon at a time, until dough comes together.Knead dough on speed 1/2 for 5 minutes.Transfer dough ball to a gallon-sized zip top bag and partially seal (don’t fully seal as the air needs to be able to escape. Place bag between layers of clean kitchen towels, then set on the floor and knead with your feet until dough has flattened. Open bag and fold flattened dough into quarters, then partially seal, wrap in the towel, and repeat again. Repeat 3-4 times until dough is very soft and smooth.Shape dough into a smooth ball, folding the edges under towards each other and pinching bottom to seal. Place in a clean plastic bag and seal, removing as much air as possible. Let sit at room temperature for 3 to 6 hours, or refrigerate overnight. If refrigerated, bring the dough to room temperature for 1 to 2 hours prior to rolling.Cut dough ball into two even pieces, and flatten each piece to a rectangle roughly 3/4-inch thick. Lightly dust with flour.Fit your KitchenAid® Stand Mixer with the pasta roller attachment set to thickness With your mixer set to speed 2, slowly feed one piece of dough through the roller. Feed it back through thickness 1 a second time. Repeat with second dough ball.For handout noodles, stop at Generously dust with flour and fold dough into thirds, then slice into noodles with a sharp chef’s knife. Unfold noodles and toss with more flour to keep noodles from sticking together.For machine cut noodles, run your dough through the roller again to thickness Swap roller for the fettuccine cutter. Dust dough sheets with flour and then run through the cutter with the mixer set to speed 3/Sprinkle noodles with flour and toss to coat.For thinner “somen” noodles, run dough again through the roller set to thickness 3, then swap roller for the spaghetti cutter. Dust dough sheets with flour and then run through the cutter with the mixer set to speed 4/Sprinkle noodles with flour and toss to coat.To cook noodles, bring a large pot of water to a gentle boil. Separate noodles a bit to keep them from sticking too much, then add to boiling water. Cook for about 5 minutes or until noodles float to the surface (thinner noodles will take less time to cook). Serve warm or, for cold noodles, rinse with cool water to stop the cooking process and keep noodles from sticking together. Drain well before serving.Fresh, uncooked noodles can also be frozen: simply spread the noodles out on a lightly floured cookie sheet and place in the freezer for 6-12 hours, then transfer noodles to a zip-top freezer bag. Cook the noodles directly from frozen, just add 1-2 minutes to the cook time.For Noodle Soup:In a medium saucepan, add sake and bring it to a boil over medium high heat for a few seconds to evaporate some of the alcohol.Reduce heat to low; add mirin and soy sauce, followed by kombu and bonito flakes. Cook for 5 minutes to allow the flavors to absorb.Turn off the heat and set aside until cool down. Strain through a fine mesh sieve to remove solids.Cook noodles according to package instructions (or, for homemade noodles, cook for 3 to 5 minutes until noodles float to the surface.) Rinse under cool water.Spoon soup base into serving bowls. Serve alongside cold noodles for dipping. Sprinkle with sesame seeds and thinly sliced green onion, if desired. Extra soup base will keep, refrigerated in an airtight container, for up to 3 days.