Wash the sweet potatoes and peel them. Chop them into 1 inch cubes. I usually chop them into thick roundels and then chop each roundel into 3/4 sticks and each stick into cubes.
I usually use the microwave to parboil the sweet potatoes. Take the chopped cubes in a microwave safe bowl, add water to cover them completely. Add turmeric powder and mix well. Microwave cook them for 10 minutes at power high.
Do not cook them more than the given time, they might turn mushy. Cook them a minute or two less, but not more than the 10 minutes. The sweet potatoes must be fork tender, when you poke them with a fork it should go through them easily.
If cooking them on stove-top, then once the water comes to a rolling boil, switch off the gas and keep it covered for 10 minutes. This should get them to fork-tender stage.
Once done, remove them from stove-top/microwave and let it sit for 2 minutes. Drain them on a colander. Let it sit until it is completely dry.