Red Onion Soup with Shiitake Broth - Meatless Monday

Ingredients

• 2 teaspoons canola or grapeseed oil
• 3 large red onions, halved and thinly sliced
• 2 teaspoons white balsamic or white wine vinegar
• 1/2 teaspoon + 1/8 teaspoon sea salt, or to taste
• 1 cup fresh thinly sliced shiitake mushrooms, stems removed
• 1 (32-fluid ounce) carton low-sodium vegetable broth
• 1/2 teaspoon freshly ground black pepper, or to taste
• 1 1/2 teaspoons minced fresh rosemary
• 1 teaspoon finely chopped fresh thyme leaves + 5 fresh thyme sprigs
• 10 whole-grain pita chips
• 1/4 cup shredded Gruyère or other aged Swiss cheese (1 ounce)