In a small bowl, whisk together the sour cream, lime juice and cumin. Transfer half of the mixture to a larger bowl and add the beef. Allow the beef to marinate, refrigerated, for at least 3 hours. Refrigerate the remaining sour cream mixture.
Preheat the oven to 425 degrees F. Once hot, put a baking sheet lined with foil in the oven for 20 minutes to heat up.
Place the beef on the hot baking sheet (a little of the sour cream mixture sticking to the beef is fine). Sprinkle the peppers and corn over top and season with salt and pepper. Roast until the beef is medium rare and the peppers are slightly tender, 8 to 10 minutes. Transfer the mixture to a bowl and keep warm.
Combine the cilantro and onions in a bowl. Warm the tortillas over a burner or in the oven.
Divide the beef and corn mixture among the tortillas, followed by the cilantro and onion mixture, jalapenos and cheese. Drizzle with the remaining sour cream mixture and serve with a lime wedge on the side.
Recipe courtesy of Geoffrey Zakarian