In a large bowl, dissolve the yeast in ¾ Cup (6 fl oz/180 ml) warm water (110°F /43°C) and let stand until foamy, about 5 minutes. Using a wooden spoon, stir in the flour, fine sea salt, and 2 tablespoons olive oil to make a soft dough. Turn the dough out onto a lightly floured work surface and knead, adding more flour as needed, until soft, smooth, and slightly sticky, about 10 minutes. Form into a ball, transfer to a lightly oiled bowl, turn to coat, and cover with a damp kitchen towel or plastic wrap. Let rise in a warm, draft-free place until doubled in bulk, about 1 hour.
Lightly oil an 8-inch (20-cm) square pan or a small baking sheet. Turn the dough out onto a lightly floured work surface and knead in the grapes. Transfer the dough to the prepared pan. Using your fingers, stretch it to cover the bottom of the square pan evenly or into a roughly 10-inch (25-cm) oval on the baking sheet. Cover loosely with a kitchen towel and let rise in a warm, draft-free place until doubled, about 1 hour.
Preheat the oven to 400°F (200°C). Brush the dough with oil and sprinkle with coarse salt. Dimple the dough with your fingertips. Bake until lightly browned, 35–45 minutes. Transfer to a wire rack and let cool for 5–10 minutes. Cut into pieces and serve.