Stir together flour and salt in a large bowl. Cut butter into flour mixture until pea-size pieces form. Gradually mix in ice water until dough comes together. Divide into 2 portions, wrap in plastic, and chill for at least 1 hour or up to 2 days.

Heat oil in a skillet over medium-high heat. Cook onion until tender, about 4 minutes. Add 1 tablespoon curry powder and cook until fragrant, about 1 minute.

Add ground turkey, soy sauce, and remaining curry powder. Cook and break up lumps until turkey is browned, about 8 minutes. Remove from heat and let filling cool completely.

Preheat oven to 450°F (230°C). Line a baking sheet with parchment paper. Roll out chilled dough to 1/8-inch thickness. Use a cutter to create circles, rerolling scraps as needed. Repeat until you make 24 circles.

Add heaping tablespoons of filling onto each circle. Fold the dough and pinch to seal edges. Place empanadas on the baking sheet about 1/2 inch apart.

Brush empanadas with egg wash made from beaten egg yolk and water. Prick each pastry to vent before baking for 15–18 minutes until golden brown.