Caramelized Mushroom Galette

Name: Caramelized Mushroom Galette
Ingredients: 1 cup whole-wheat flour; 3/4 cup all-purposed flour, plus more for dusting; 1 1/2 teaspoons kosher salt, divided; 1/3 cup plus 3 tablespoons olive oil, divided; 1/3 cup water; 2 teaspoons red wine vinegar, divided; 1 medium red onion; 1 pound fresh mushrooms, such as cremini, shiitake, or oyster mushrooms, or a combination; 1 small bunch fresh rosemary; 1/4 teaspoon freshly ground black pepper, divided; 1 tablespoon Dijon mustard; 4 ounces Brie cheese