Minced beef, onions, carrots, and potatoes in a curry-spiced sauce.
For the Beef Filling:
1 tablespoon (8g) cornstarch
1/2 cup (120ml) water
3 tablespoons (45ml) vegetable or other neutral cooking oil, divided
8.8 ounces (250g) ground beef, at least 20% fat
Kosher salt
1/2 small yellow onion (1.7 ounces; 50g), finely diced
2 small Yukon gold or yellow potatoes (4.2 ounces; 120g total), peeled and cut into 1/2-inch dice
1 small carrot (2.6 ounces; 75g), peeled and cut into 1/4-inch dice
1 teaspoon Nigerian-style curry powder (see note)
1 teaspoon dried thyme
1 cup (235ml) Nigerian-style stock or water
1/2 small green bell pepper (1.7 ounces; 50g), stemmed, seeded, and finely chopped, divided
Freshly ground black pepper
For the Dough:
5.6 ounces all-purpose flour (160g; 1 1/4 cups)
1 ounce whole wheat flour (30g; 1/4 cup)
1 teaspoon (3g) Diamond Crystal kosher salt; for table salt, use half as much by volume or the same weight
1/2 teaspoon baking powder
3.1 ounces unsalted butter (90g; 6 tablespoons), cold
1 large egg (1 1/4 ounces; 50g), lightly beaten
1/4 cup (60ml) ice-cold water, plus more as needed
To Assemble and Bake:
1 large egg yolk (15g) lightly beaten with 1 tablespoon (15ml) milk (any fat percentage)
For the Beef Filling: In a small bowl, whisk cornstarch with 1/2 cup (120ml) water until well combined and set aside.
In a 10-inch cast iron or stainless-steel skillet, heat 1 tablespoon oil over medium heat until shimmering. Add ground beef, season lightly with salt, and cook, stirring and breaking up chunks of meat, until beef is no longer pink, about 5 minutes. Transfer to medium heatproof bowl and set aside.
Add remaining oil to now-empty skillet and continue to heat on medium until shimmering. Add onion, potatoes, and carrot, season with salt, and cook, stirring occasionally, until just beginning to soften, about 4 minutes. Add curry powder and thyme and cook, stirring frequently, until fragrant, about 2 minutes.
Add cooked beef along with the stock or water, cover, and bring to a boil. Reduce heat to maintain a simmer and cook, stirring once or twice, until vegetables are softened, 12 to 15 minutes.
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Stir in half of the green bell pepper and cook until just softened, about 2 minutes. Stir cornstarch slurry to redistribute the starch, then stir into the beef mixture. Bring to a simmer and cook, stirring occasionally, until beef and vegetables are coated in a thickened sauce, about 5 minutes. Stir in remaining green bell pepper and season with salt and pepper to taste. Transfer to medium heatproof bowl and set aside to cool, about 30 minutes (filling can be refrigerated in an airtight container for up to 3 days).
For the Dough: Meanwhile, in a large bowl, whisk together all-purpose flour, whole wheat flour, salt, and baking powder until thoroughly combined.
Using the large holes of a box grater, grate butter over flour mixture. Using your hands, toss grated butter with flour mixture until butter is evenly distributed.
Make a 4-inch wide well in the center of the butter-flour mixture. Whisk beaten egg and ice-cold water together until combined. Pour egg mixture into well, then, using a flexible spatula, gradually stir butter-flour mixture into egg mixture until a cohesive dough forms with visible bits of butter. If dough is too dry, add additional water, 1 tablespoon at a time, until dough comes together. Shape dough into a flat, round disk, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes or up to 2 days.
Set dough disk on a generously floured work surface. Portion into 6 equal-sized balls (2 1/3 ounces; 65g each). Using a rolling pin and adding more flour as needed underneath and on top of dough to prevent sticking, roll out each ball into a 6-inch circle about 1/8 inch thick. Transfer rounds to a lightly-floured rimmed baking sheet and cover loosely with plastic wrap to prevent dough rounds from drying out.
To Assemble and Bake: Line a rimmed baking sheet with parchment paper. Working with one dough round at a time, set on a lightly-floured work surface and add 1/2 cup (3 1/2 ounces; 98g) of beef filling to bottom half of the round, leaving a 1/2-inch border along the edge. Fold top half over the filling to form a semicircle, then press down gently around the edge to seal. Using the back tines of a fork, press down firmly around the edge to ensure meat pie is well sealed. Transfer to a prepared baking sheet and cover loosely with plastic wrap. Repeat the process with remaining dough rounds and filling. Cover loosely and refrigerate at least 30 minutes and up to 2 hours.
Twenty minutes before baking, adjust oven rack to middle position and preheat to 400°F (205°C). When ready to bake, brush surface of pies with egg wash. Poke pies all over with a fork, 5 to 6 times each. Bake meat pies, rotating tray halfway through, until golden brown on all sides, about 25 minutes. Let cool for 10 minutes.
Transfer meat pies to a serving platter and serve warm or at room temperature.