Butter Chicken Hand Pies

• 1/3 cup plain whole milk strained (Greek-style) yogurt
• 1 tablespoon grated fresh ginger (from 1 [3-inch] piece), divided
• 1 tablespoon grated garlic (from 6 large cloves), divided
• 2 teaspoons Kashmir chile powder, divided
• 2 teaspoons garam masala, divided
• 2 teaspoons kosher salt, divided
• 1 pound boneless, skinless chicken thighs (about 3 to 4 thighs), cut in half
• 3 tablespoons unsalted butter
• 3/4 cup chopped yellow onion (from 1 small [6-ounce] onion)
• 1/2 teaspoon ground cumin
• 1/2 cup tomato puree
• 3/4 cup plus 1 tablespoon heavy whipping cream, divided
• 3/4 cup frozen sweet peas
• 1 large egg
• 1 (14-ounce) package all-butter frozen puff pastry (such as Dufour), thawed and chilled

All-purpose flour, for dusting

Nigella seeds, for garnish

1. Stir together yogurt, 1 teaspoon of the ginger, 1 teaspoon of the garlic, 1 teaspoon of the Kashmiri chile powder, 1 teaspoon of the garam masala, and 1 teaspoon of the salt in a medium bowl until evenly combined. Add chicken and mix until evenly coated in yogurt mixture. Cover and refrigerate for at least 30 minutes or up to 24 hours (preferably overnight).
2. Melt butter in a large skillet over medium. Add onion and cook, stirring occasionally, until softened and starting to brown on edges, 6 to 8 minutes. Add cumin and remaining 2 teaspoons ginger, 2 teaspoons garlic, 1 teaspoon Kashmiri chile powder, and 1 teaspoon garam masala; cook, stirring often, until fragrant, 1 to 2 minutes. Add marinated chicken (discard any yogurt mixture left in bowl), and cook, stirring occasionally, until opaque but not fully cooked through, 4 to 5 minutes. Stir in tomato puree, 3/4 cup of the cream, and remaining 1 teaspoon salt; bring to a simmer over medium. Cover, reduce heat to medium-low and simmer, stirring occasionally, until chicken is cooked through and easily shreds with a fork, 10 to 12 minutes.
3. Remove from heat and carefully shred chicken using 2 forks. Return to a simmer over medium and simmer, stirring occasionally, until slightly thickened, 3 to 5 minutes. Stir in peas and remove skillet from heat. Transfer to a shallow bowl and refrigerate until completely cooled, about 30 minutes (once cooled, filling can be covered and refrigerated for up to 3 days).
4. Line a large rimmed baking sheet with parchment paper; set aside. Stir together egg and remaining 1 tablespoon cream in a small bowl; set aside. Working quickly, roll out puff pastry to a 20- x 12-inch rectangle on a lightly floured work surface with short edge facing you; dust puff pastry with flour as needed to prevent sticking. Slice in half horizontally to create 2 (10- x 12-inch) halves. Slice each half into 3 (10- x 4-inch) rectangles.
5. Spoon about 1/2 cup chicken mixture onto bottom half of each rectangle, leaving a 3/4-inch border along bottom and sides. Working with 1 rectangle at a time, lightly brush bottom and side border of puff pastry with egg mixture. Fold top half of puff pastry over filling, and gently press edges together to seal. Crimp edges using a fork. Gently transfer hand pies to prepared baking sheet, spacing evenly apart. Brush hand pies with egg mixture. Cut 2 (3/4-inch) slits on top of each hand pie using a paring knife. Sprinkle evenly with nigella seeds. Freeze until firm, about 30 minutes. Meanwhile, preheat oven to 425°F.
6. Remove hand pies from freezer, and bake at 425°F until hand pies are slightly puffed and lightly browned on top, about 15 minutes. Reduce oven temperature to 375°F, and bake until hand pies are puffed, browned, and crisp, 20 to 25 minutes. Let stand 10 minutes before serving.