Add the potatoes to boiling water and simmer for 15-20 minutes, until soft, mash and set aside.
Soften the leeks in a pan with butter.
Preheat the oven to 200°C
Mix the milk and flour in a saucepan and add the fish. Simmer on a low heat for 5 minutes. Place the leek into the mixture and stir well.
Add the fish, leeks and sauce mixture into an oven-proof dish, and add the potato onto the top.
Bake in the oven for 20-25 minutes at 200°C
Place the broccoli and green beans into boiling water and simmer until tender.