Step 1

For the red curry paste: In a food processor, combine the cilantro, oil, ginger, lemongrass, coriander, cumin, shrimp paste, garlic, red chiles, lime leaf, 1 teaspoon salt and 1 teaspoon pepper. Pulse to a consistent paste.

Step 2

For the curry: Heat 2 tablespoons of the oil in a large Dutch oven over medium heat. Add the curry paste and cook, stirring well, until aromatic, about 2 minutes. Transfer to a bowl and set aside. Add the remaining 2 tablespoons oil to the pot and increase the heat to high. Sprinkle the flank steak with a pinch of salt, then add it to the pot; cook for 3 to 4 minutes. Remove the steak and add the onions and peppers; cook until tender, 2 to 3 minutes. Add the coconut milk, bring to a gentle boil, then add the curry paste back to the pot; stir well. Reduce the heat and simmer for about 15 minutes. (If the coconut milk breaks and separates, don't worry: it will come back together to a smooth consistency.) Add the chicken broth and fish sauce, and continue simmering until the sauce has a nice, gravy-like consistency, 12 to 15 minutes. Return the beef to the pot and finish with the cilantro, basil, mint and lime juice. Taste and adjust the seasoning.