How to Make It
In a large, shallow bowl, combine the sesame oil with 1/4 cup of the sugar and 2 tablespoons of salt. Add the beef and stir to coat with the marinade. Let stand at room temperature for 1 hour.
In a medium saucepan, combine the water with the tamarind concentrate, fish sauce and the remaining 1/4 cup of sugar and bring to a boil. Cook over high heat, stirring occasionally, until the sugar is dissolved and the sauce is reduced to 1 cup, about 12 minutes. Season with salt and remove from the heat; keep warm.
In a large skillet, heat the vegetable oil until shimmering. Add the shallots and cook over moderately high heat until browned and crisp, about 2 minutes. Using a slotted spoon, transfer the shallots to a plate.
Add half of the shallot oil to another large skillet and heat both skillets. Drain the meat and add one-fourth to each skillet in an even layer without crowding. Cook over high heat, turning once, until browned, about 2 minutes. Using a slotted spoon, transfer the meat to a platter. Repeat with the remaining meat. Pour the warm tamarind sauce over the meat, top with the fried shallots and serve.
Tamarind concentrate is available at Asian markets and at specialty-food stores.