recipe is in James Peterson's <i>Vegetables</i>:
trim dark greens from, split lengthwise, rinse the grit from
1 bunch of leeks
line in oblong tian or gratin dish, the pour over
1 c heavy cream
bake in oven 375F for 1 hr, taking out now and then to tamp down and moisten with the boiling cream. i imagine it'd be good with creme fraiche as well.