In the work bowl of the food processor, combine the semolina flour, unbleached all-purpose flour, yeast, salt, and sugar. Pulse until it’s all mixed together. While the machine is running, slowly pour in the warm water and olive oil, and process until it’s all mixed and you have a dough that is silky-smooth. It may feel slightly to very sticky, depending on humidity. If it’s too wet, as in runny, add another tablespoon or so of all-purpose flour and process until it’s mixed in.
Turn the dough out onto a floured surface and lightly turn it over a couple times to make the dough smooth, elastic, and satiny. Cover with a cloth and let it rest for 15 minutes.
Punch the dough down, turn it over, and divide into 4 or 6 equal pieces. Flatten each piece into a round about 1/4-inch (0.64 cm) tall. Lay a piece of parchment (optional) on a large pizza peel or the back side of a baking sheet and sprinkle it with additional semolina and lay the rounds on it, side by side. Cover with a tea towel and let rise in a warm place until doubled, about 45 minutes.
While the dough is rising, position the oven rack on the lowest rung in the oven and place the baking stone on it. Preheat the oven to 400° F/200° C.
Press the center of each round with the palm of your hand to deflate it, then prick with a fork a couple times. The loaf should hold its shape. Brush each round with the melted butter. Immediately slide Immediately slide the loaves onto the hot stone and bake until the tops are golden and the loaves sound hollow when tapped on the bottom, about 15 to 20 minutes. Transfer to a towel-lined board to cool.