In a large bowl, whisk together flour, yeast, and 2 teaspoons (6 grams) salt with a dough whisk until combined. Add 1½ cups (360 grams) warm water and 2 tablespoons (28 grams) oil, stirring just until combined. Cover and let stand in a warm, draft-free place (75°F/24°C) until puffed, 1½ to 2 hours.
Preheat oven to 400°F (200°C).
Turn out dough onto a lightly floured surface, and shape into a ball. Line a rimmed baking sheet with parchment paper. Brush parchment with 1 tablespoon (14 grams) oil. Transfer dough to prepared pan, and gently press or roll dough into a 14×12-inch rectangle. Cover and let rest for 10 minutes.
Coat dough generously with remaining 2 tablespoons (28 grams) oil. Sprinkle with sugar, and top with Concord grapes, pressing gently into dough. Sprinkle with rosemary and remaining 1 teaspoon (3 grams) salt.
Bake until golden brown, 30 to 35 minutes. Let cool for 30 minutes before slicing.
Notes
*You do not have to seed the grapes. The heat from the oven helps break the seeds down as the focaccia bakes.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/concord-grape-focaccia/