Put the potatoes in a large pot and cover with cold water; add the salt and bring to a boil, uncovered. Simmer until fork tender, about 15 minutes.
Meanwhile, place a large skillet over medium flame. Add the chorizo, and cook, stirring for 5 minutes, until the sausage renders its fat and gets crispy. Add the onion and garlic; season with the cumin, oregano, salt, and pepper. Cook and stir for 5 minutes, until the mixture is soft and has a beautiful red color. Pour in the broth and simmer for 3 minutes.
Drain the potatoes and fold them into the pan, using a wooden spoon, break up the potatoes into nickel-size pieces. Add the olives and raisins and toss everything together; season with salt and pepper, to taste. Allow the filling to cool before filling the empanadas. Serve with cilantro cream.
In a large bowl, sift together the flour, masa harina, baking powder, and salt. Stir in the melted butter. Gradually add 1/2 cup to 3/4 cup of water, working it in with your hands to incorporate; the dough should be easy to handle and not sticky. Form the dough into a ball, wrap it in plastic, and chill for 30 minutes.
Lightly flour your rolling pin and counter. Divide the dough in 1/2 so it will be easier to work with and roll it out to 1/8-inch thickness. Using a 4-inch cookie or biscuit cutter, cut out 10 circles of dough; repeat with the other 1/2.
Spoon 2 generous tablespoons of filling into the center of each pastry circle, leaving a 1/2-inch border. Brush the edges with the egg wash and then fold the dough over in 1/2 to enclose the filling and form a semi-circle. Tightly seal the edges by crimping with the tines of a fork. Chill at least 30 minutes before baking.
Preheat the oven to 375 degrees F. Place the empanadas on a buttered baking sheet and brush the tops with additional egg wash. Using a fork, prick a few holes in the top of the empanadas for steam to escape. Bake for 30 minutes, until the pastry is golden brown.
1 cup sour cream
1/4 cup finely chopped fresh cilantro leaves
1/2 lime, juiced Kosher salt and freshly ground black pepper
In a small mixing bowl, combine the sour cream, cilantro, and lime juice together. Mix thoroughly; season with salt and pepper. Serve with empanadas.