Okra and Potato Salad

Name: Okra and Potato Salad
Ingredients: 3 tablespoons lemon juice; 1 tablespoon sherry vinegar; 3/4 pound small potatoes, preferably fingerlings, scrubbed and sliced about 1/2-inch thick; Salt; Black pepper; 1 pound okra; 1 serrano pepper, seeded if desired, minced; 1 shallot, minced, soaked for 5 minutes in cold water, and drained; 1 garlic clove, puréed in a mortar and pestle with a pinch of salt; 1/4 cup plain yogurt; 1/4 cup olive oil; 1/4 cup chopped parsley; 1 to 2 ounces crumbled feta for serving (optional)