Spiced plum pie

Ingredients

• 1 kg dark-fleshed plums
• 1/2 cup brown sugar
• 1/4 cup cornflour
• 1/2 tsp cinnamon
• zest of 1 orange
• 2 tbsp semolina
• 1 egg white
• 1 tbsp demerara sugar, optional
• Pastry
• 2 1/2 cups plain flour
• 1 tbsp sugar
• 1/2 tsp salt
• 220 g butter, cubed
• 1/4 cup cold water
• 2 tsp white vinegar