Add the sodium carbonate to the warm water and mix until dissolved.
Add the bread and all purpose flours together with the salt in the bowl of a stand mixer. Using the dough-kneading attachment, turn the mixer on to low. Slowly add the water, about a quarter quantity at a time, over the course of 30 seconds. The dough should begin to come together after a couple of minutes, but it will be quite shaggy. If the dough isn’t coming together, add one tablespoon of water at a time until it does, but remember you are not trying to achieve the consistency of a normal pasta dough; ramen dough should be quite dry and difficult. Your mixer should appear as if it's struggling and the dough should be shaggy.
This is the point at which you decide whether or not to risk the motor of your stand mixer. Since this dough is extremely tough, it is very taxing on the mixer’s motor. After my dough comes together (2-3 minutes), I turn it onto my countertop and knead by hand for an additional 8 minutes. You will curse and sweat, and if you aren’t then carry on but add less water next time. All in all, you want to get a good ten minutes worth of kneading time in, regardless of whether you carry on with your stand mixer or knead by hand.
After you’re finished kneading, form the dough into a vague ball and wrap it in cling film or pop it in a zip-loc baggy for an hour at room temperature.
After an hour, the texture will have softened considerably. Divide the dough into 7 approximately 125 gram pieces or 6 approximately 150 gram pieces, depending on how big you want your noodle portions to be (the former is more than enough for a hungry me).
Remove one piece of dough from the bag/cling film, keeping the remaining pieces covered until it’s their turn to be squashed. Use your hand to press the dough into an oblong shape.
Starting on the widest setting of a pasta machine, roll the dough through. Fold it over on itself and run it through once more. Don’t worry if the edges are a little bit rough to start.
Continue running the dough through the machine until the noodles are as thin as you desire them to be. The cooking times below assume you are making your noodles a notch or two thicker than the middle setting. Liberally dust the ramen sheet with some cornflour on both sides. Cut the sheet according to how long you want your noodles to be. Run the sheet through a spaghetti-making attachment and dust with more cornflour.