Potato and Pea Samosas

Name: Potato and Pea Samosas
Ingredients: 3 tablespoons vegetable oil; 1/2 teaspoon mustard seeds; 2 1/2 ounces chopped onion; 1 teaspoon finely chopped ginger; 2 1/2 ounces frozen peas; 1 tablespoon ground coriander; 1 teaspoon ground cumin; 1/4 teaspoon red chile powder; 1/2 to 3/4 teaspoon garam masala; 1 to 2 teaspoons dried mango powder*; Kosher salt; Splash water; 1 pound 5 ounces potatoes, peeled, boiled until soft, and crushed into large lumps; 4 tablespoons chopped fresh cilantro leaves; 1 package frozen phyllo pastry dough, thawed; 5 tablespoons melted butter, for brushing; 2 tablespoons sesame seeds, poppy seeds or nigella, optional