Place a large cast iron griddle or pan on the stove, on high heat.
Add about 2 teaspoons of tallow or ghee to the steak and rub all over.
Very generously season the steak with salt and pepper.
Place the steak onto the hot griddle/pan and cook for about 5 min per side.
Remove from heat and let rest while you prepare the tortillas.
In a small pot/pan on high heat, add about 2 tablespoons ghee or tallow. When the oil heats up, add a tortilla for about 10 seconds per side and place onto a paper towel-lined plate to absorb excess oil.
Repeat with remaining tortillas and add more ghee/tallow to the pot as needed.
Slice the steak against the grain and then cut the strips into smaller 1-inch pieces for the tacos.
Assemble the tacos: Add steak, onion, and cilantro to a tortilla. Squeeze a bit of lime onto each taco. Top with hot sauce and Mexican crema or sour cream. Enjoy!