Cut beef across the grain into 1⁄4-inch-thick slices. Place in a large zip-top plastic bag. For marinade, in a small bowl, combine beef broth, vinegar, soy sauce, and chili-garlic sauce. Pour into bag with beef. Squeeze out air and seal. Gently massage to combine ingredients. Marinate in the refrigerator for at least 2 hours or overnight.
Soak 6-inch wooden skewers in water for at least 1 hour.
For Sweet Chili Dipping Sauce: In a medium saucepan, combine sugar, vinegar, Thai seasoning, chili-garlic sauce, and salt. Bring to a boil over medium-high heat; reduce heat. Simmer for 5 to 10 minutes or until sugar is dissolved, stirring occasionally. Transfer to a bowl and cool.
Remove beef from the marinade; discard marinade. Drain skewers. Thread beef, accordion style, onto skewers. Preheat broiler. Place skewers on a wire rack over a foil-lined baking sheet or broiler pan. Broil 6 to 8 inches from heat for 4 to 6 minutes or until beef is cooked through, turning halfway through broiling. Sprinkle with sesame seeds (optional). Serve with dipping sauce.
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