Really, the best way to eat a flank steak is perfectly seared (a la Amanda and Merrill). But I also love a steak taco, and flank steak fits the bill perfectly. You can enjoy this steak and sauce the way I outline below, or without the pineapple, or cabbage, or the corn shell or either of the three. The sauce is strong, but a flank steak holds up to it well and it's always fun to eat your meat with your hands. —lizb
Preheat the oven to 400°. Cut the cherry tomatoes in half and toss them in 2 tablespoons of olive oil. Roast them, cut side up, for 20 minutes.
In the mean time, caramelize the onions by sauteing them in the other two tablespoons of oil over low heat for about 30 minutes.
When the tomatoes and onions are done, put them, and the rest of the sauce ingredients in a food processor or blender and pulse a few times until blended through, but not totally pureed. The sauce is best when a left a little chunky. It can be made ahead of time and held in the refrigerator for a few days.
Flank Steak Tacos
Follow Amanda and Merill's instructions to sear a flank steak - or sear it on a nice hot grill. When the steak is cooked, baste it with the sauce and let it rest for five to ten minutes. In the mean time grill the pineapple slices and chop into bite sized pieces, and chop the cabbage. Heat the corn tortillas in a pan, or in the microwave in a towel for about 15 seconds, until pliable.
When the steak has rested, slice it as thin as possible. Pile a few slices on a corn tortilla, top with pineapple, cabbage, and garnishes. Pour a margarita and chow down!