Vegan Roasted Broccoli Soup

Name: Vegan Roasted Broccoli Soup
Ingredients: 2 small or 1 large crown broccoli (12 to 15 ounces); 2 tablespoons plus 1/2 teaspoon olive oil, divided, plus more for serving; 1 1/4 teaspoons kosher salt, divided, plus more as needed; 6 large unpeeled cloves garlic; 1 medium yellow onion; 1/2 medium head cauliflower (about 12 ounces); 2 medium Yukon gold potatoes (about 12 ounces total); 1/2 teaspoon freshly ground black pepper; 1 (32-ounce) carton low-sodium vegetable broth; 1/2 bunch fresh parsley; 1/2 medium lemon; 2 tablespoons nutritional yeast; 1 heaping cup croutons, for serving (optional)