In large bowl, dissolve granulated sugar in warm water. Sprinkle in yeast; let stand for 10 minutes or until frothy. Whisk in 2 tbsp of the oil and salt. With spoon, stir in 3 ½ cups of the flour until smooth. Gradually stir in enough of the remaining flour to form soft dough. Turn out onto floured surface; knead until smooth and elastic, 8 to 10 minutes, dusting with as much of the remaining flour as necessary to prevent sticking. Place in greased bowl, turning to grease all over. Cover with plastic wrap; let rise in warm place until doubled in bulk, about 1 ½ hours.
Punch down dough; turn out onto floured surface. Divide in half. Flatten each half to ½ inch thickness. Place each in greased 8-inch round cake pan, press in grapes. Brush with remaining oil. Cover with plastic wrap; let rise until doubled in bulk, about 1 hour.
Sprinkle with coarse sugar. Bake in centre of 400°F oven until golden, about 40 minutes. Remove from pans; let cool on rack.