Steak Skewers with Scallion Dipping Sauce

INGREDIENTS

• 2 tablespoons palm sugar or (packed) light brown sugar
• 2 tablespoons chinkiang (black) vinegar
• 3 tablespoons fish sauce (such as nuoc nam or nam pla)
• 1 1 1/2" piece ginger, peeled
• 1 cup canned unsweetened coconut milk
• 4 red or green Thai chiles, stemmed
• 1/4 cup fish sauce (such as nuoc nam or nam pla)
• 15 scallions, very thinly sliced
• 2 pounds tri-tip, top sirloin cap steak, or rib eye, fat cap left on
• 2 garlic cloves, crushed
• 6 garlic cloves
• 1 tablespoon fresh lime juice
• 1 1/2 tablespoons fresh lime juice
• 2 tablespoons toasted sesame seeds
• 1/2 cup canned unsweetened coconut milk
• 2 lemongrass stalks, bottom third only, tough outer layers removed
• 3 tablespoons grapeseed oil