Grape and Rosemary Focaccia

Name: Grape-and-Rosemary Focaccia
Ingredients: 14 ounces seedless red grapes; ⅓ cup plus 1 tablespoon extra-virgin olive oil, plus more if needed; 4 ¾ cups unbleached bread flour, plus more for dusting; 2 ¼ cups warm water (about 110 degrees); ½ cup plus 2 tablespoons raisins; ½ cup plus 2 tablespoons golden raisins; ¾ teaspoon active dry yeast (not rapid rise; from one ¼-ounce envelope); 1 tablespoon plus 1 ½ teaspoons kosher salt; 3 tablespoons fine sanding sugar; 2 tablespoons fresh rosemary; Flaky sea salt, for sprinkling