To make the stock, combine the beef bones and 2 litres/2 quarts of water in a stockpot and bring to a boil. Drain, then rinse the bones. This assures a clear broth.
In the same stockpot, combine the bones, garlic, celery, nutmeg, salt and pepper. Add 2 litres/2 quarts of water and bring to a boil. Reduce the heat to medium-low, then cover and simmer for 2–3 hours. Strain the broth into a medium saucepan and set aside.
To make the sambal,bring a small saucepan of water to a boil. Add the chillies, garlic and sugar and boil for 6–8 minutes, until softened. Reserve 4 tablespoons of the water, then drain. Transfer the mixture to a blender and blend until smooth. If needed, add the reserved water to loosen the mixture to the desired consistency. Season to taste with salt.
To make the meatballs, heat the oil in a small frying pan over medium heat. Add the garlic and sauté for 1–2 minutes until golden brown. Set aside.
In a blender or food processor, combine the fried garlic, meat and pepper and process until fine. Add the egg, tapioca flour and 50ml/¼ cup cold water and mix until smooth.
Fill a saucepan halfway with water and bring to a simmer. Scoop a small handful of the meatball mixture in one hand and make a gentle fist. Gently squeeze the paste up through the hole between your thumb and index finger until you have a small ball about the sizeof a large grape. Scoop the meatball with your other hand and gently lower it into the pan. Repeat with the remaining mixture. Simmer the meatballs for 6–7 minutes until they float to the surface. Using a slotted spoon, remove one of the meatballs and cut it in half to check that it’s cooked through.
Put the meatballs into the broth and bring to a boil. Reduce the heat to medium-low and simmer for 10 minutes.
To make the noodles, prepare the noodles according to the package directions. Drain, then transfer to a bowl of cold water. Drain again, then set aside.
Add the pak choy to the broth and cook for 45 seconds. Using a slotted spoon, transfer the pak choy to a plate.
Place the noodles into individual bowls and add the pak choy. Top with 3–4 meatballs, then ladle 2 spoons of broth into each bowl. Season each bowl with vinegar, tomato sauce, soy sauces and Sriracha. Sprinkle with crispy shallots and celery leaves. Serve immediately with the sambal.
The meatballs are traditionally minced by hand, using two cleavers on a chopping board to create a fine meatball paste. Still, it’s time-consuming (and, arguably, dangerous for the uninitiated). A blender or food processor works perfectly well in the home kitchen. It’ll serve you well to prepare a big batch of the meatballs and freeze them when you need a quick topping for fried rice, noodles or stir-fried vegetables.
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