Spring Green Soup

Ingredients

• 1 bunch Swiss chard, about 2 pounds, rinsed and stemmed
• 1 bunch dandelion greens, about 1 1/2 pounds, rinsed and stemmed
• 1 tablespoon butter
• 2 scallions, chopped
• 1 clove garlic, minced
• 1/2 teaspoon chopped chili pepper
• 2 cups chicken broth
• 1 cup thinly sliced fresh fennel
• 1 cup peeled and cubed potatoes
• 1/2 teaspoon sugar
• 1/2 teaspoon salt
• 1/4 teaspoon white pepper
• 2 tablespoons chopped fresh mint, plus mint for garnish if desired
• 1 cup milk
• 1 cup yogurt, plus yogurt for garnish if desired
• 1 cup grated feta cheese