To make the filling, in a medium saucepan, combine the potatoes, ½ teaspoon salt and 6 cups water. Bring to a boil over high and cook until a skewer inserted into the potato meets no resistance, 15 to 18 minutes. Drain in a colander, shaking to remove as much water as possible, then return the potatoes to the saucepan. Set the pan over low and allow the potatoes to dry for about 1 minute. Remove the pan from the heat, add 1 tablespoon butter and, using a potato masher, mash until the mixture is mostly smooth; set aside.

In a 12-inch nonstick skillet over medium, melt the remaining 1 tablespoon butter. Stir in the onion, cover and cook, stirring occasionally, until lightly browned and softened, about 8 minutes. Add the tomato paste and cook, stirring, until the paste begins to brown, 1 to 2 minutes. Stir in the jalapeños, garlic and grated tomatoes, followed by the ground beef, cumin, coriander and ½ teaspoon salt. Cook over medium-high, breaking the beef up into small bits, until the meat is no longer pink and the mixture begins to sizzle, about 15 minutes.

Remove the pan from the heat. Add the mashed potatoes and stir until fully integrated, then stir in the cilantro. Taste and season with salt and pepper. Transfer to a medium bowl and cool to room temperature, then cover and refrigerate until chilled while you make the dough, or for up to 24 hours.

To make the dough, in a stand mixer with the paddle attachment, mix both flours and the salt on low until combined, about 30 seconds. With the mixer running on low, drizzle in the butter, then add the yogurt. Mix on low until a smooth dough forms, about 5 minutes; if there are still dry bits at the bottom of the bowl, mix in water 1 tablespoon at a time until the bits are integrated and the dough is smooth. Lightly flour the counter, then turn the dough out onto it. Briefly knead the dough, forming it into a ball. Divide in half, form each piece into a 6-inch disk, wrap in plastic and refrigerate for at least 1 hour or up to 24 hours.

When you are ready to form the empanadas, remove the dough from the refrigerator and let stand at room temperature for about 15 minutes. Line 2 rimmed baking sheets with kitchen parchment. Lightly flour the counter, then, using a rolling pin, roll one portion of dough into a round about 1/16 inch thick. Using a 4-inch round cutter, cut out 12 circles, gathering the scraps and re-rolling the dough as needed. Place the circles on one of the prepared baking sheets, overlapping them slightly to fit; cover with a kitchen towel. Repeat with the second portion of dough.

Remove the filling from the refrigerator. Have ready a small bowl of water. Set one dough circle on the counter. Mound 4 teaspoons filling onto the center of the lower half of the circle and, with your fingers, slightly flatten the mound, keeping the edges of the dough clear. Using your finger dipped into the water, very lightly moisten the edge of half the dough circle along the arc closest to you. Fold the unfilled side over the filling, aligning the edges and forming a half moon; lightly press on the filling to flatten it slightly and remove any air pockets. Press the edges with your fingers, then with the tines of a fork to create a secure seal and a decorative edge. Place the empanada on the second prepared baking sheet. Using the remaining dough circles and filling, form additional empanadas. Cover with plastic wrap and refrigerate for at least 30 minutes or for up to 2 hours.

To fry the empanadas, set a wire rack in a rimmed baking sheet and set it near the stove. Pour oil into a large (7- to 8-quart) Dutch oven to a depth of about 1½ inches and heat over medium-high until the oil reaches 350°F. Carefully lower 6 empanadas into the oil and cook, stirring occasionally, until golden brown, 2 to 3 minutes. Using a slotted spoon, transfer the empanadas to the prepared rack. Return the oil to 350°F and cook the remaining empanadas in the same way. Serve warm.

Spicy Green Salsa (Ají): In a medium bowl, combine the scallions, chili, bell pepper, cilantro, vinegar, lime juice and 1 teaspoon salt. Cover and refrigerate for at least 1 hour or for up to 1 day. Start to finish: 20 minutes, plus chilling. Makes 2 cups.