I think his original idea is to reduce the milk cream mixture with the long cooking, but I think the top would be too burnt. So the temperature should be lowered if need to be cooked for 1.5 hour.
For the leftover of the leek pudding, I add some grated parmesan, and reheated in oven, it was even better. To improve the dish, I think no need to cook the leek beforehand for 30 minutes, maybe 10 minutes is enough, the leeks disappeared with so much cooking.
The next recipe I will try next week is the sausage breakfast casserole in simply recipes, looks delicious, it will be dinner rather than breakfast though. I will post the result.