Combine the water and yeast in the bowl of an electric mixer fitted with the dough hook. Let sit for 1 minute to let the yeast dissolve. Add the flours, sugar, and salt and mix on low speed for about 30 seconds, until well incorporated. Slowly add ½ cup of olive oil and mix on medium speed for 4 to 5 minutes, until the dough comes together to form a smooth ball. Transfer the dough to a lightly oiled bowl and turn to coat evenly. Cover the bowl with a clean dish towel and let rise in a warm, draft-free area for 2 to 3 hours, until doubled in volume.
Sprinkle some cornmeal onto a large rimmed baking sheet. Place the dough on the baking sheet and gently stretch to fit into the pan. Cover with the dish towel and let rest for another hour, until soft and puffy.
Preheat the oven to 425°F. Poke the dough all over with your fingertips, then sprinkle the grapes, olives, and rosemary over the surface of the dough. Drizzle the remaining ¼ cup of olive oil over the dough. Bake for about 30 minutes, until the bread is golden brown and the grapes and olives are softened. Remove from the oven and let cool slightly before serving.