Thanksgiving Stuffing Focaccia

Name: Thanksgiving Stuffing Focaccia
Ingredients: 2 tablespoons unsalted butter; 4 stalks celery, finely diced; 1 onion, finely diced; 1/4 cup fresh sage leaves, finely chopped; 2 chicken bouillon cubes, crushed (see Cook’s Note); Coarsely ground black pepper; 6 cups all-purpose flour (see Cook's Note); One 1/4-ounce package active dry yeast (2 1/4 teaspoons); 2 teaspoons sugar; 2 1/2 cups warm water (80 to 85 degrees F); 1/2 cup plus 1 teaspoon extra-virgin olive oil; Kosher salt; 1 cup fresh parsley leaves, finely chopped; 1 pound sweet Italian sausage, removed from casing; Nonstick cooking spray, for the plastic wrap, optional; Flaky sea salt, for sprinkling; 3 tablespoons extra-virgin olive oil