To prepare the blackberry mostarda, in a large bowl, combine the blackberries, sugar and mustard seeds and cover with cheesecloth. Let stand at room temperature overnight. 

Strain all of the liquid from the blackberry mixture into a saucepan and bring to a boil. Remove from the heat and let the liquid cool for 5 minutes, then pour back over the fruit. Repeat this process for 3 days. 

On the fourth day, in a small bowl, whisk together the canola oil and dry mustard. Strain the liquid from the blackberry mixture into a pot and reduce the liquid to a syrupy consistency. Stir in the canola oil mixture and combine with the blackberry mixture. Serve the mostarda as a condiment with the empanadas. It also makes a great complement to cheese, latkes and meats.

To prepare the dough, in a large bowl, whisk together the flour and salt. Using a pastry blender or a fork, cut in the lard until the flour mixture resembles chunky sand.

Make a well in the center of the flour and add the vinegar and about 3/4 cup of the cold water. Stir with a fork until a shaggy dough forms. If all of the flour has not been moistened, add the remaining water 1 tablespoon at a time.

Turn the dough out onto a work surface and gently knead until smooth. Divide the dough into 12 equal pieces and roll out 1/8 inch thick. Using a cookie cutter or tracing a bowl with a knife, cut into rounds. 

The dough rounds can be filled immediately and baked. If not using immediately, stack the rounds on top of each other, with a piece of parchment paper in between each one, and refrigerate.

To prepare the filling, in a large sauté pan over medium-high heat, warm the canola oil. Add the duck breast and cook, stirring occasionally, for 2 minutes. Add the mushrooms and season with salt and pepper. Add the onion, garlic, cumin, turmeric and piment d'Espelette and cook, stirring occasionally, for 3 minutes. Add the tomato paste and currants and cook, stirring occasionally, for 2 minutes. Add the wine, reduce the heat and cook until the liquid is reduced. Transfer the filling to a rectangular baking dish and refrigerate until cool.

Preheat the oven to 350°F.

To assemble the empanadas, place 2 tablespoons of the filling in the center of each dough round. Fold it in half and crimp the edges. In a small bowl, whisk the egg and brush the egg wash over the top and the crimps of the empanadas. Place the empanadas on a baking sheet.

Transfer to the oven and bake until golden brown, 18 to 20 minutes. Serve hot with the blackberry mostarda.