Rub the 225g cold cubed butter into the 250g flour and 1/2 tsp salt until the mixture is shaggy with flat butter flakes. Add the 90ml ice cold water gradually until the dough just holds together. Shape into a rectangle, wrap, and refrigerate for 30 minutes.

Combine the diced apples, 75g granulated sugar, 1 tbsp cornstarch, 1 tsp cinnamon, 1/4 tsp nutmeg, 1/4 tsp salt, and 1 tbsp lemon juice in a medium saucepan over medium heat. Cook for 8 to 10 minutes until thickened and glossy. Remove from heat, stir in 1 tbsp butter, and spread on a plate to cool completely.

Roll the chilled dough to 3mm thickness and cut into 12 rectangles of about 13cm x 10cm. Place 6 on a parchment-lined baking sheet, add 2 tablespoons of filling to each, egg-wash the borders, top with the remaining rectangles, and seal the edges firmly with a fork.

Heat the oven to 220°C (425°F). Brush the tops with beaten egg, add 1 tbsp coarse sugar, and cut 2 slits in each pie. Bake for 18 to 20 minutes until deep amber and blistered.

Rest on a wire rack for 3 to 4 minutes, then arrange on a serving plate, dust with a pinch of cinnamon, and serve warm.