Heat 1/2 of the butter in a frying pan over medium heat. Cook shallots for 5 minutes. Add the leeks and carrots and cook for 2 minutes. Add white wine and cook uncovered for 10 minutes. Season with salt and pepper to taste.
In the meantime, heat the remaining butter in another frying pan over high heat. When the butter starts to brown add the scallops to the frying pan. Cook the scallops one minute on each side.
Add crème fraiche to the leeks and stir.
Place some leeks and carrot on each plate and then add two scallops per plate.