Combine sourdough discard, cold water, and one egg in a small bowl and mix until smooth. Keep chilled until use.
In a large bowl, mix flour, baking powder, and salt. Add cold butter cubes and coat with flour, breaking them down to walnut- and pea-sized pieces.
Make a well in the flour and butter mixture, pour in the chilled starter liquid, and mix lightly with a spatula until just combined. Knead lightly by hand until dough holds.
Shape dough into a disc, wrap in plastic wrap, and refrigerate for 30 minutes.
Roll the chilled dough into a 10x12 inch rectangle, fold shorter edges to the center like a letter, wrap, and refrigerate for at least 2 hours or overnight.
Heat oil in a skillet over medium-high heat. Fry potatoes 5 minutes, then add carrots and ground beef, cooking until beef browns and vegetables are tender, about 5-10 minutes.
Stir in garlic powder, smoked paprika, salt, black pepper, raisins, and frozen peas. Adjust seasoning and cool filling completely.
Preheat oven to 400°F. Line baking sheets with parchment paper.
Divide dough into 12 equal portions (about 2 oz each) and chill 15 minutes wrapped in plastic.
Roll each dough ball into a 6-inch disc. Add 3 tablespoons filling to half, fold over, trim excess dough, and crimp edges with a fork. Place on baking sheet and chill until all are shaped.
Brush each empanada with beaten egg wash (egg mixed with salt).
Bake empanadas for 15-20 minutes until golden. Cool slightly before serving.
Store leftovers in airtight container refrigerated for up to 3 days or freeze unbaked for up to 3 months.