01 - Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
02 - In a large mixing bowl, combine ground beef, egg, breadcrumbs, minced garlic, spring onions, soy sauce, salt, and black pepper. Gently mix until just incorporated, avoiding overworking the mixture.
03 - Form the mixture into 20 to 24 small meatballs of even size and arrange them on the prepared baking sheet.
04 - Bake for 12 to 15 minutes, or until meatballs are cooked through and attractively browned.
05 - While the meatballs bake, combine hot sauce, brown sugar, honey, apple cider vinegar, soy sauce, and sriracha (if using) in a saucepan. Set over medium heat and bring to a gentle simmer, stirring until the sugar dissolves.
06 - Reduce heat and stir in unsalted butter until fully melted and the sauce takes on a glossy sheen.
07 - Transfer baked meatballs to a large bowl. Pour the hot firecracker sauce over and toss gently to evenly coat.
08 - Serve meatballs immediately, garnished with sesame seeds and additional sliced spring onions.