Mix garlic, steak seasoning, smoked paprika, chipotle or cumin, hot sauce, Worcestershire sauce and vinegar. Whisk in extra-virgin olive oil. Place meat in shallow dish and coat it evenly in marinade. Let stand 15 minutes.
Cut larger potatoes in half, leave very small potatoes whole. Place potatoes in a pot and cover with water. Bring to a boil and cook potatoes 12 to 15 minutes until tender.
Heat a grill pan or outdoor grill to high heat.
Cut leek in half lengthwise. Chop into 1/2-inch pieces. Place leeks in big bowl of water and release all the dirt from them with a good swish, separating all the layers. Drain leeks in a colander.
Grill flank steak 6 to 7 minutes on each side.
Put a drizzle of extra-virgin olive oil into a hot nonstick skillet over medium high heat. Cook bacon 3 to 5 minutes until it begins to crisp and has rendered most of its fat. Add leeks to the skillet and cook 3 to 5 minutes more until the leeks are tender.
Drain the potatoes and return them to the hot pot. Smash the potatoes with the chicken stock. Add the BLT: bacon, leeks and tomatoes to the potatoes and continue to smash. Season the potatoes with salt and pepper to your taste.
Remove flank steak from grill and let juices redistribute before slicing. Thinly slice meat on an angle, cutting the meat against the grain. Serve sliced flank steak next to BLT potatoes and top potatoes with a dollop of sour cream.