Layered Grapes and Bread with Chèvre and Balsamic

Name: Layered Grapes and Bread with Chèvre and Balsamic
Ingredients: For the bread:; 10 ounces day-old sourdough, cut into 1-inch cubes (8 to 9 cups); 2 tablespoons olive oil; 2 teaspoons minced garlic; 2 teaspoons fresh thyme; 1/2 teaspoon fresh ground black pepper; For everything else:; 2 large sweet onions (1 pound total); 2 teaspoons olive oil, plus extra for the dish; 3 tablespoons port, divided; Kosher salt; 1/3 cup balsamic vinegar; 1 pound organic seedless black grapes, de-stemmed and halved (about 4 cups), divided; 1 1/2 cups homemade or low-sodium chicken stock or vegetable broth; 4 1/2 ounces chèvre; 1/4 cup grated Parmesan