Jamie Oliver's Fish Pie

for the mashed potato topping

• 1 kg potatoes peeled and chopped into large chunks
• 400 g frozen peas
• 2 tablespoons butter
• Zest of 1 lemon
• salt & pepper to taste

for the fish pie filling

• 500 ml 2 cups milk
• 1 bay leaf
• 200 g frozen hake fillets
• 200 g frozen smoked haddock fillets
• 200 g frozen shelled prawns
• 2 onions finely chopped
• 2 carrots finely chopped
• 2 garlic cloves finely chopped
• 3 tablespoons flour
• 1 heaped teaspoon English mustard
• 40 g 1/2 cup mature cheddar, grated
• Juice of 1 lemon
• salt & pepper to taste
• 2 onions finely chopped
• 2 carrots finely chopped