Combine the flour and salt in the bowl of a food processor. Cut in the butter, pulsing a few times until the mixture is like coarse meal with pea-sized lumps. Add the eggs, white vinegar, and 1/3 to 2/3 cup cold water, continuing to pulse just until the dough comes together. Transfer the dough to a work surface, form into a flat disk and wrap tightly in plastic wrap. Chill in the refrigerator for 1 hour, while making the filling and yogurt sauce.
For the filling:
Toast the chile powder, coriander and cumin in a skillet until fragrant. Add the jalapenos, sweet potatoes and black beans. Season to taste with salt.
For the yogurt sauce:
Combine the yogurt, lemon juice and zest, cilantro and cumin in a small bowl and mix. Season to taste with salt. Cover and refrigerate until ready to use.
Preheat an oven to 400 degrees F.
Portion the dough into 10 balls. On a floured work surface, roll each dough ball into a 6-inch circle. Spoon 3 to 4 tablespoons of filling into the center of each circle. Brush the edges with egg wash before folding the dough over to create a crescent shape. Press and seal edges. Cut 3 slits across the top of each empanada and brush the tops of each with egg wash. Bake until golden brown, about 25 minutes. Serve with the yogurt sauce.
Instructions for freezing:
Follow instructions for building empanadas, but do not brush the tops with the egg wash. Place built empanadas on a parchment-lined baking sheet and put into the freezer. Once the empanadas have frozen, place them in a plastic re-sealable bag and return to the freezer for up to 2 weeks.
Instructions for reheating:
Preheat the oven to 400 degrees F. Place the frozen empanadas on a parchment-lined baking sheet. In a small bowl, whisk one whole egg and brush over the tops of the empanadas. Bake until golden brown and heated through, 35 to 40 minutes.