To begin, preheat your oven to 375°F (190°C). In a large bowl, mix the flour and salt. Add the chilled, diced butter and, using your fingers or a pastry cutter, blend until the mixture resembles coarse crumbs. This step ensures a flaky crust.

In a separate bowl, whisk the egg and cold water together, then pour it into the flour mixture. Stir until the dough comes together, adding a little more water if necessary. Wrap the dough in plastic wrap and chill for 30 minutes.

While the dough is chilling, heat olive oil in a skillet over medium heat. Add the onion, bell pepper, and garlic, and sauté for 5-6 minutes until softened and fragrant. This step builds the flavour base of the filling.

Add the ground beef or shredded chicken to the skillet, breaking up any lumps. Cook until browned and fully cooked through, about 7-8 minutes. Stir in the tomato sauce, smoked paprika, salt, and pepper. Allow to simmer for another 5 minutes, reducing any excess liquid.

Stir in the sliced olives and chopped hard-boiled egg, mixing until well combined. Remove from heat and let the filling cool to room temperature. This step prevents the dough from becoming soggy when assembled.

On a floured surface, roll out the chilled dough to about 1/8 inch thick. Use a round cutter or a small bowl to cut circles, approximately 4 inches in diameter. This step ensures uniform empanadas that bake evenly.

Place a spoonful of the cooled filling in the centre of each dough circle. Fold the dough over to form a half moon shape, pressing the edges firmly. Seal by crimping with a fork or twisting the edges. Transfer the assembled empanadas to a baking sheet lined with parchment paper.

Brush the tops of the empanadas with beaten egg yolk for a golden finish. Bake in the preheated oven for 20-25 minutes or until the empanadas are golden brown. Serve warm, garnished with extra olives or a side of Spanish aioli for dipping.