01 - Preheat oven to 425°F. Line a baking sheet with parchment paper.
02 - In a large mixing bowl, combine ground beef, egg, breadcrumbs, minced garlic, finely chopped spring onions, soy sauce, salt, and black pepper. Mix gently until just combined, avoiding overmixing.
03 - Shape the mixture into 20 to 24 small meatballs and arrange them evenly on the prepared baking sheet.
04 - Bake meatballs for 12 to 15 minutes, or until thoroughly cooked and golden brown on the outside.
05 - While the meatballs are baking, combine 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 fully dissolves.
06 - Reduce heat to low and whisk in unsalted butter until melted, resulting in a glossy, emulsified sauce.
07 - Transfer cooked meatballs to a large bowl. Pour hot firecracker sauce over the meatballs and toss until each is evenly coated.
08 - Arrange on a serving platter, then garnish with sesame seeds and sliced spring onions. Serve immediately.