Fry off the leeks (sliced) with a little bit of butter.
Once the butter has melted and the leeks are translucent add a tbsp of flour and stir so they are fully coated.
Slowly pour the milk in until the flour is dissolved.
Bring the milk to a simmer for 5mins adding bay leaves and some pepper.
Add in the frozen vegetables and bring up to a simmer again.
Cut the fish into square pieces and stir into the sauce.
Cook for another 10mins. Try avoiding stirring so the fish doesn't break up.
Whilst the fish is cooking steam the broccoli and carrot so that they can be added to the sauce already cooked.
Next add in the prawns along with the steam broccoli and carrot. Stir gently letting the sauce thicken for a further 5 minutes.
Once the sauce is a thick and creamy consistency and the fish is cooked through, transfer to a pie dish.
Combine the breadcrumbs and cheese together.
Sprinkle the crumble topping all over the pie and season before placing under a medium-hot grill for 2-5 minutes until the topping is golden and the sauce bubbling.
Serve with extra vegetables whilst piping hot!