Pour cold water (two and 1/2 cups for each cup of cornmeal) into a large pot. Over high heat, begin to bring to a boil.
After a few minutes, when the water is warm, slowly add the about half the cornmeal to the water one spoonful at a time, stirring continuously with a sturdy wooden spoon. Continue cooking (and stirring) until the mixture begins to boil and bubble. Reduce heat to medium and cook for a few minutes.
Cooking the mixture over medium heat, add the remaining cornmeal, as before, sprinkling it spoonful by spoonful as you continue to stir. It is essential to keep stirring -- if making a large quantity, it may take one person to hold the pot and another to use two hands to stir.
The nshima should be very thick (no liquid remaining) and smooth (no lumps). It may reach this point before all of the remaining cornmeal is added to the pot -- or it may be necessary to add even more cornmeal than this recipe indicates.
Once the desired consistency is reached, turn off heat, cover the pot, and allow the nshima to stand for a few minutes before serving. Serve nshima immediately, hot, with the ndiwo of your choice.
With clean hands, tear bits of nshima off and use them to scoop up the ndiwo.