01 - Preheat oven to 425°F. Line a baking sheet with parchment paper.
02 - In a mixing bowl, blend ground beef, egg, breadcrumbs, minced garlic, spring onions, soy sauce, salt, and black pepper. Combine just until ingredients are evenly incorporated; avoid overmixing.
03 - Portion and shape the mixture into 20 to 24 uniform meatballs. Arrange them evenly on the prepared baking sheet.
04 - Bake for 12 to 15 minutes until meatballs are browned on the outside and cooked through.
05 - While meatballs are baking, combine hot sauce, brown sugar, honey, apple cider vinegar, soy sauce, and sriracha (if using) in a saucepan. Heat over medium, bringing the mixture to a simmer while stirring until the sugar is completely dissolved.
06 - Reduce the heat and whisk in the unsalted butter until melted, resulting in a glossy finish.
07 - Transfer the hot meatballs to a large bowl. Drizzle the firecracker sauce over them and toss gently to ensure even coverage.
08 - Arrange meatballs on a serving dish, then sprinkle with sesame seeds and sliced spring onions. Serve at once.