Anna Thomas Green Soup

Name: Anna Thomas' Green Soup
Ingredients: 1 bunch chard or spinach; 1 bunch kale; 4 to 5 green onions, sliced, white and green parts; 1/2 cup loosely packed cilantro; 1 teaspoon sea salt, plus more to taste; 1 medium Yukon Gold potato; 1 medium yellow onion; 1 1/2 tablespoons olive oil; Marsala or dry sherry (optional); 1 to 2 cloves garlic, finely chopped; 2 1/2 to 3 cups vegetable broth; Freshly ground black pepper; Cayenne; 1 tablespoon fresh lemon juice, plus more to taste