Method

• 1.
  For the pastry, place flour, cumin, butter and 3/4 tsp salt flakes in a food processor and pulse until a crumb texture (you still want some chunks of butter). Add lemon juice and 100ml cold water and pulse until dough comes together. Wrap in plastic wrap and refrigerate overnight.
• 2.
  To make the filling, heat the oil in a large saucepan over medium-high heat. Cook onion, stirring occasionally, for 5 minutes until golden. Add garlic and ginger and cook, stirring constantly, for 1 minute.
• 3.
  Add paste and cook, stirring constantly, for 2 minutes. Add chicken and stir until well coated. Cook for 5 minutes. Add tomatoes and 2/3 cup (160ml) water, scraping bottom of pan with a spoon. Add potato and bring to the boil. Reduce to a simmer and cook, covered, for 40 minutes or until potatoes are tender when pierced with a fork. Mix cornflour with 1 tbs water in a small bowl until smooth. Add to pan and cook, stirring constantly, for 2 minutes until sauce boils and thickens. Check seasoning. Transfer to a bowl and set aside to cool slightly. Chill for 2-3 hours until cold.
• 4.
  Preheat oven to 200°C/180°C fan-forced.
• 5.
  When ready to bake, stir peas, chopped coriander and garam masala through filling. Spoon into a 7-cup capacity baking dish.
• 6.
  Roll out pastry on a generously floured benchtop until a little wider than your dish. Place over the filling. Press edges. Trim any surplus pastry with a knife. Press a fork around the edges to decorate. Whisk yolk and milk in a small bowl and brush over pie top. Sprinkle with freshly ground black pepper. Make several incisions on top of the pie for steam to escape. Bake for 35-40 minutes until pastry is well golden.
• 7.
  Stand for 10 minutes before serving with extra coriander sprigs.