Position your top oven rack in the second slot from the top and preheat the broiler to high. Line a large rimmed baking sheet with aluminum foil. Meanwhile, place your 12-inch cast iron skillet over medium-high heat.

In a medium bowl, whisk together the sour cream, mayonnaise, and 1 tablespoon of taco seasoning until smooth. Set aside.

Place your flank steak on the prepared baking sheet. Brush both sides evenly with olive oil. Sprinkle 1 tablespoon of taco seasoning over one side, then season generously with sea salt. Flip the steak and repeat with the remaining tablespoon of seasoning and more salt.

Slide the steak under the broiler for 5-7 minutes, flipping once at the halfway mark. For medium-rare, aim for an internal temperature of 130-135°F.

While the steak broils, add two corn tortillas to your hot cast iron skillet. Let them warm for 30 seconds to a minute until they develop some color, then flip and repeat. Transfer to aluminum foil and continue with the remaining tortillas, wrapping them to keep warm.

When your steak is done, remove it from the oven and let it rest for 5 minutes. After resting, slice the steak against the grain into thin strips. Transfer to a medium bowl and toss with the fresh lime juice.

Stack two tortillas together. Add a generous portion of the seasoned steak, then pile on your favorite toppings. Finish with a dollop of the seasoned crema and serve immediately with lime wedges on the side.