1-First Step: Prepare the Pie Dough
In a large mixing bowl, combine 350 g plain flour and 1 teaspoon salt. Add the cold, cubed 230 g butter (dairy or dairy-free) and quickly rub it into the flour using your fingertips or a pastry blender until the mixture resembles coarse crumbs with some small butter bits. Gradually add the 75 ml cold water, one tablespoon at a time, mixing gently until the dough just comes together. Form the dough into a disk, wrap with cling film, and refrigerate for at least 1 hour. This resting helps maintain the dough’s flakiness during baking.

2-Second Step: Prepare the Filling
Heat half the butter (15 g) together with 15 ml olive oil in a pan over medium heat. Add the chopped leek and optionally minced garlic, sautéing for about 5 minutes until softened. Add the mushrooms in batches if needed and cook until browned and moisture evaporates. Stir in remaining butter, ½ teaspoon salt, ½ teaspoon pepper, and fresh thyme or dried mixed herbs. Add a pinch of ground nutmeg if desired. Cook for another 10 minutes until the mixture is cooked through and well combined. Remove from heat and allow to cool. Drain any excess liquid to avoid soggy pastry.

3-Third Step: Assemble the Hand Pies
Roll out the rested dough on a lightly floured surface to approximately 5 mm thickness. Cut into rectangles roughly 15 cm by 9 cm. Place a generous spoonful of the cooled leek and mushroom mixture on one half of each rectangle, leaving an edge margin. Sprinkle crumbled feta cheese evenly over the filling. Brush edges with egg yolk wash or vegan glaze. Fold dough over to cover the filling and press edges together firmly with fingers or a fork to seal. Cut two small slits on the top of each pie to vent steam.

4-Final Step: Bake and Serve
Preheat your oven to 220°C (430°F) or 200°C (390°F) if using vegan puff pastry. Place the hand pies on a parchment-lined baking sheet and chill for 30 minutes to help maintain shape and flakiness. Before baking, brush tops and sides with egg wash or aquafaba, and sprinkle optional seeds on top. Bake for 20-25 minutes or until golden brown and puffed. Remove from oven and cool slightly before serving warm or at room temperature.