Sauté leeks in
oil with a pinch of salt for 10 minutes. Add carrots, parsnips, turnips and
thyme and sauté for 5 more minutes. Season to taste with salt and pepper.
Transfer vegetables
to a casserole or gratin pan.
Pour milk over vegetables;
then cover with Parmesan cheese.
Cover and bake for 15
minutes. Remove cover and bake another 30 minutes until golden brown.