Add the bread flour, salt, yeast, and sugar. Process to blend them. Add the Greek yogurt, and then add the whey (or water) through the feed tube while the food processor is running, adding the liquid as fast as the flour will absorb it. Continue processing until the dough form a ball.
Turn off the processor and let the dough sit for 10 minutes or so. Then process again for another minute. Check to see if the dough had become smooth (relatively - there are seed bits, so it won't be completely silken) and elastic and no longer sticky. If it isn't done, continue processing. You might need to redistribute the dough in the bowl so it all gets kneaded.
If the dough starts feeling warm, stop processing and let it rest and cool before processing further.
When the dough has doubled, knead it briefly, form it into a ball, and put it back in the bowl. Cover the bowl with plastic wrap and let it rise again, until doubled.
Sprinkle a baking sheet with cornmeal and preheat the oven to 325 degrees.
Take the dough out of the bowl, form it into a tight ball, and place it, seam-side down, on the baking sheet. Cover with plastic wrap and let it rise until doubled.
When the dough has risen, brush it with the eggwash and sprinkle with sesame seeds (if desired), Slash the dough in an X pattern across the top and down the sides, and bake at 325 degrees for 40-45 minutes.