Courtesy of Cook's Illustrated. Easy and delicious!

Beef
4 Tbsp vegetable oil
4 Tbsp packed dark brown sugar
2 Tbsp fish sauce
1 (1.5-1.75 lb) hangar or flank steak, cut against the grain into pieces that are approximately 4"x2"x1/4"

Basting Sauce
3/4 cup coconut milk
3 Tbsp packed dark brown sugar
3 Tbsp fish sauce
2 Tbsp vegetable oil
3 shallots, minced
2 stalks lemongrass, trimmed to bottom 6 inches and minced
2 Tbsp grated fresh ginger
1.5 tsp ground coriander
3/4 tsp red pepper flakes (or 3 fresh thai chilis)
1/2 tsp ground cumin
1/2 tsp salt

Process
Whisk beef marinade ingredients together (oil, sugar, and fish sauce).
Toss beef with marinade and let stand at room temperature for 1-2 hours.
Weave beef onto 12" metal skewers, 2 or 3 pieces to a skewer.

Meanwhile, prep basting sauce ingredients and whisk together in a small bowl.
After basting sauce has sat for awhile, strain solids and retain.

Prepare a hot grill with the coals close to the grates.
Cook skewers for approximately 4 minutes per side, basting with basting sauce liquid.
Optional: on the stovetop, cook down the basting sauce solids to make an accompanying sauce.

Serve with a peanut sauce.