Creamy White Bean Soup with Lemony Yogurt and Crispy Leeks | America's Test Kitchen

Ingredients

• 1 leek, white and light green part only
• 2 tablespoons all-purpose flour
• 1/2 cup vegetable oil
• 1/2 cup plain Greek yogurt
• 3 tablespoons water
• 1 teaspoon grated lemon zest plus 2 teaspoons juice
• 2 tablespoons extra-virgin olive oil
• 1/2 cup chopped onion
• 1 small celery rib, chopped fine
• 3 sprigs fresh thyme
• 2 garlic cloves, sliced
• Pinch cayenne pepper
• 2 (15-ounce) cans great Northern beans
• 2 tablespoons grated Parmesan cheese
• 2 cups chicken broth, divided
• 2 tablespoons unsalted butter
• 1/2 teaspoon lemon juice, plus extra for seasoning