Method

1. Slice the flank steak across the grain into thin strips and then as needed into 1 ½ to 2-inch pieces and put in a large bowl. In a medium bowl, combine the kroeung, chili paste, curry powder, fish sauce, kosher salt, and palm sugar, mixing well. Add to the steak along with the annatto oil and, using your hands turn the beef, separating the slices to coat  each piece in the marinade. Let sit at room temperature for 30 minutes.
2. To prepare the pickled papaya, in a large bowl toss the papaya and carrot together. Cut the cucumbers in half widthwise and then into slices. In a small bowl, combine the fish sauce if using, salt, brown sugar, and lime juice. Pour over the papaya mixture. Add the shallot, garlic, and ginger, and toss to combine.
3. Preheat a charcoal or gas grill to medium-high heat. Soak the bamboo skewers in water for 15 minutes to keep them from burning.
4. In a medium bowl, whisk the coconut cream, curry powder, and annatto oil together and set aside.
5. Thread the slices of beef onto the skewers, using 2 slices per skewer. Grill the skewers until well-marked on the first side, 1 ½ to 2 minutes. Turn, brush on the coconut-annatto sauce and grill until the underside is well marked, 1 ½ to 2 minutes. Turn the skewers again and brush the other side with the sauce. Continue to grill until the beef is cooked through, 1 to 2 minutes more.
6. Serve hot with the pickled papaya on the side.