1. Preheat oven to 200C/Gas 6
2. Bring a large pan of salted water to the boil, then add the leeks and cook for 5 minutes.
3. When the leeks are cooked, drain and place into a buttered oven proof dish. Pile the salmon over the leeks.
4. Melt the butter in a small pan and add the flour. Cook, stirring for one to two minutes until lightly golden.
5. Remove from the heat and gradually whisk in the milk to form a smooth sauce. Return to the heat, stir and simmer for 2-3 minutes.
6. Remove from the heat and beat in the egg yolks, mustard and season with salt and pepper. Pour over the leeks and salmon. Top with the grated cheese.
7. Place in the oven and cook for 10 minutes, until golden brown. Serve immediately.
Recipe courtesy of