Seafood Pie with Potato Pastry

Ingredients

• 1 cup all-purpose flour
• 1/2 tsp ground turmeric
• 1/2 cup mashed potato
• 100 g margarine (chilled and diced)
• 1 tbsp 1% milk (to glaze)
• 1 tbsp dried breadcrumbs
• 400 g skinless white fish fillets
• 200 g peeled shrimp or seafood mix
• 2 leeks (trimmed and thinly sliced)
• 3/4 cup frozen peas (thawed)
• 2 tbsp fresh flat-leaf parsley (chopped)
• 2 sprigs fresh thyme (leaves)
• 1 lemon (zest grated)
• 1/4 cup cornstarch
• 2 cups 1% milk