01 - Preheat oven to 425°F (220°C) and line a baking sheet with parchment paper.
02 - Combine ground beef, egg, breadcrumbs, garlic, spring onions, soy sauce, salt, and black pepper in a mixing bowl. Mix until just combined to maintain tenderness.
03 - Form mixture into 20 to 24 small, evenly-sized meatballs and arrange on prepared baking sheet.
04 - Bake meatballs for 12 to 15 minutes until they are cooked through and well-browned.
05 - While meatballs bake, combine hot sauce, brown sugar, honey, apple cider vinegar, soy sauce, and sriracha in a saucepan over medium heat. Stir constantly and bring to a simmer until sugar dissolves.
06 - Reduce heat and stir in unsalted butter until melted and the sauce is glossy.
07 - Transfer baked meatballs to a large bowl. Pour hot firecracker sauce over the meatballs, tossing gently to coat each piece evenly.
08 - Arrange meatballs on a serving platter and sprinkle generously with sesame seeds and sliced spring onions. Serve immediately.