Spread baking soda on a lined baking tray and bake it for about an hour at 250F. This causes your sodium bicarbonate to chemically decompose to sodium carbonate, which is more alkaline. That alkalinity is essential to achieving the texture, color, and flavor of a ramen-style noodle. It's kinda impractical to bake 4 tsp of baking soda honestly, so I would recommend doing a larger batch and storing it. I actually baked off about 1/2 cup as you can see in the photo.
Dissolve 4 tsp of your sodium carbonate into the warm water. It's easier to dissolve if you whisk it in slowly.
Add the cold water and flour. Mix well.
Knead the dough for 5 minutes, then wrap it in plastic and set it aside for 20 minutes. This is a tough dough to knead, so it might be a long 5 minutes, but keep at it.
Unwrap the dough and repeat step 4.
Knead for 5 minutes once more, then wrap and chill for 1 hour.
The dough is ready now, but when you make your noodles, you'll wanna pull it out of the fridge and let it warm up for awhile before trying to work it.
Get your pasta maker ready. Cut off about 1/3 of the dough, flatten it a bit, and roll it through on the widest setting.
Work the dough down with your pasta machine. You'll have to guess and experiment a little to find the thickness you like.
Once you've got a nice, long strip of dough, cut it. Some pasta machines include a cutter, but you can always roll your dough and slice it by hand if you don't have one.
If you toss your noodles with a little cornstarch to keep them from sticking, and seal them in a plastic bag, they store pretty well in the freezer.
Generally, boil these noodles in salted water for 2-5 minutes. You'll have to adjust to the size you've cut them, and whether or not they're frozen. About 1 minute before they're cooked through, strain them out and rinse with cold water, then drop them in a pot of hot broth and they'll be done by the time they get to the table.
