1. Mix the sour cream and hot sauce, and set aside for later use.
2. In a large skillet, heat the butter over medium heat. Add in the onions and cook, stirring only occasionally, until deep brown and caramelized, 20 minutes. Season with salt and pepper and set aside.
3. Heat a large, cast-iron grill pan over medium-high heat. Sprinkle the steaks liberally with salt and pepper. Cook the steak until super caramelized, 5 to 6 minutes per side. Rest the meat for 10 minutes.
4. While steaks are cooking, whisk the eggs with a couple pinches salt and pepper. Quickly scramble the eggs until slightly firm. Set aside.
5. Thinly slice the rested steaks, removing any large pieces of fat. On a flat tortilla, sprinkle layer of gruyere, then add on some sliced steak, scrambled eggs and finally some caramelized onions. Roll up, brush with a little vegetable oil and griddle for 2 to 3 minutes per side.
6. Serve with a sidecar of the prepared sour cream.