01 - Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper for easy removal and cleanup.
02 - In a large bowl, combine ground beef, egg, breadcrumbs, minced garlic, chopped spring onions, soy sauce, salt, and black pepper. Gently mix until ingredients are just incorporated without overworking the mixture.
03 - Form the mixture into 20 to 24 evenly-sized small meatballs. Arrange on the prepared baking sheet, spacing them apart. Bake for 12 to 15 minutes until well-browned and fully cooked.
04 - While meatballs are cooking, place hot sauce, brown sugar, honey, apple cider vinegar, soy sauce, and sriracha (if using) in a saucepan over medium heat. Stir and bring to a simmer until the sugar is dissolved.
05 - Reduce heat to low and stir in unsalted butter. Continue stirring until butter is melted and the sauce is smooth and glossy.
06 - Transfer baked meatballs into a large bowl. Pour the hot firecracker sauce over the meatballs and toss gently to coat all sides evenly.
07 - Arrange sauced meatballs on a serving platter. Sprinkle with sesame seeds and sliced spring onions. Serve immediately.