In a large saucepan, blanch the sliced leeks in salted boiling water for 1 minute; drain well.
Melt 3 tbsp of the butter in the same saucepan over medium heat and add the leeks.
Cook the leeks in the butter for 15-20 minutes, until they are very soft and beginning to break down.
Add the clementine zest and curry powder, and cook a couple minutes longer to meld the flavors.
Blend in the crème fraîche and remove from the heat.
In a large skillet, melt the remaining butter over medium-high heat.
Season the scallops on both sides with salt and pepper.
When the butter is hot, add the scallops and sear - about two minutes each side.
While the scallops are cooking, reheat the creamy leeks.
Divide the leeks between two dinner plates, top with the scallops, and serve with a lightly dressed green salad.