Melt butter and a splash of olive oil in a heavy-bottomed pan over low heat. Add leeks, thyme and garlic and slow cook until they are "soft and sweet", about 20 minutes. Turn up heat, add wine. Let wine reach a boil, add beans, and a little water (enough to almost cover beans). Simmer gently for 5-10 minutes. Add parsley, creme fraiche, and a nice toss of good olive oil. Taste for seasoning.
Heat another heavy-bottomed cast-iron or griddle pan under a hot broiler. Season meat with salt and pepper and drizzle with a bit of olive oil. Sear steaks under the broiler for 2-3 minutes on each side for medium-rare. Remove from pan to a serving platter and let it rest for 5 minutes. Squeeze some lemon juice and drizzle some olive oil over meat. Carve steaks into thick slices. Divide beans on dinner plates and place steak on top. Drizzle with some of the resting juices.