Make Pastry

For pastry, in a medium bowl combine flour, baking powder, and the 1/4 teaspoon salt. Using a pastry blender, cut butter into flour mixture until mixture resembles coarse crumbs. Sprinkle 2 tablespoons of the cold water over part of the flour mixture; toss gently with a fork. Push moistened pastry to a side of the bowl. Repeat moistening flour mixture, using 2 tablespoons of the cold water at a time, until flour mixture is moistened.

Gather flour mixture into a ball, kneading gently until it holds together. Wrap dough in plastic wrap and chill for 30 minutes.

Cook Potatoes

Meanwhile, for filling, in a small saucepan cook potatoes, covered, in enough boiling salted water to cover for 10 to 15 minutes or until tender; drain and set aside.

Cook Lamb and Onion

In a large skillet cook lamb, onion, and garlic over medium heat until lamb is no longer pink and onion is tender. Drain off fat. Return lamb mixture to skillet. Stir in cooked potatoes, peas, cilantro, cumin seeds, and the 1/2 teaspoon salt. Heat through. Set aside.

Assemble Pastes

Preheat oven to 425°F. Grease a baking sheet and sprinkle it lightly with cornmeal; set aside. In a small bowl lightly beat together egg and the 1 tablespoon water; set aside. Divide dough into six equal-size portions. On a lightly floured surface, roll each portion into a 7-inch circle. Place 2/3 cup of the filling on the bottom half of each dough circle. Moisten edges of pastry circles with some of the egg mixture; fold pastry over filling. Press edges together with a fork to seal.

Transfer pasties to prepared baking sheet. Brush pasties evenly with the remaining egg mixture. Make a small slit in the top of each pasty to let steam escape.

Bake and Serve

Bake pasties for 10 minutes. Reduce oven temperature to 350°F. Bake for 30 to 35 minutes more or until golden brown. Serve warm or at room temperature. Serve with salsa verde.