Stir the yeast and water together in a large bowl. Using a wooden spoon and stirring in one direction, stir in the whole wheat flour about a cup at a time; then stir 100 times or until the mixture look smooth and silky. This is the sponge and it needs to rest, covered with plastic wrap, for at least 30 minutes, although it is best if it can rest for as long as 8 hours in a cool place, a rest that will give fuller flavor. Sprinkle the slat over the sponge and then stir in the olive oil, mixing well, again stirring in the same direction. Add the flour about a cup at a time, mixing until the dough is too stiff to stir with a spoon. Turn the dough out onto a lightly floured work surface and knead it mixing until it is smooth and elastic, 8 to 10 minutes. The dough will be moderately firm and have a slight sheen. Clean the mixing bowl, dry it, and coat it lightly with oil. Transfer the dough to the bowl, turn the dough around to oil its surface, and cover tightly with plastic wrap. Let the dough rise at room temperature for 2 to 3 hours, or until it doubles in bulk. Turn the dough onto the work surface. Divide it in half and keep one half under plastic or cloth while you work with the other. Cut the dough into 8 equal pieces and, with lightly floured cupped hands, form the pieces into tight balls; keep the balls under plastic as you work on the other.
On a well-floured surface, flatten the balls of dough with you fingertips and then, using a rolling pin, roll each piece of dough into a circle 8 to 9 inches in diameter and less than 1/4-inch thick. Cover but do stack the rolled out breads. Preheat the griddle or cast-iron skillet over medium-high heat and lightly oil the griddle. Bake 1 rolled-out circle at a time on the griddle, putting the pita top side down on the griddle and cooking for 15 to 20 seconds before turning the bread over gently. Cook for another minute or until big bubbles appear. Turn the bread again and cook until it balloons fully. Pressing a towel on those areas where bubbles have formed will push air into the flat areas. The breads should bake for no more than 3 minutes. Oil the griddle after every 4 to 5 breads. Pita is best the day it is made, but it can be wrapped airtight and frozen for 1 month