• In a small bowl, sprinkle the yeast onto the water and stir together with the sugar. Let the mixture rest until the yeast blooms, 3 to 4 minutes.
• Combine yeast mixture, 3 cups of the flour, and the salt, in stand mixer. Mix well, then change to the dough hook and gradually add more of the flour, kneading well between each addition, until the dough is smooth, fairly firm, and no dough sticks to the side of the bowl, about 5 minutes.
• Pour all but 2 tablespoons of the olive oil onto a 12 x 16 ½ -inch baking sheet. Simply lift the dough from the bowl and gently stretch and press it to fit the pan. Drizzle the dough with the remaining olive oil and dimple the top of the bread with your fingertips. Press the grapes into the dough evenly all over the bread, leaving about one inch between grapes. Sprinkle the bread generously with the chopped rosemary and coarse salt. Bake the focaccia until it is a nice crisp brown, about 30 minutes. Remove from the oven and cut with a pizza cutter into squares.