Mix flour and salt together. Add warm water and start kneading the dough with your hands. Since masa harina absorbs water slowly, you’ll need to knead the dough for at least 5 minutes. If, after kneading for a few minutes, the dough still seems dry and crumbly, add 2 Tbsp. warm water at a time and knead for a few minutes before adding any more. The finished dough should feel soft, slightly sticky, and smooth.