To prepare the broth, place beef bones in a stockpot with 2 liters (2 quarts) of water. Bring to a boil, then discard the water and rinse the bones to remove impurities—this ensures a clear, clean-tasting broth.

Return the cleaned bones to the pot and add garlic, celery, nutmeg, salt, and white pepper. Pour in another 2 liters of fresh water and bring to a boil again. Lower the heat to medium-low, cover the pot, and let it simmer gently for 2 to 3 hours. Once done, strain the broth into a separate saucepan and set aside.

To make the sambal, bring a small saucepan of water to a boil. Add the chilies, garlic, and sugar, and boil for 6 to 8 minutes until the ingredients have softened. Reserve 4 tablespoons of the boiling liquid, then drain the rest. Transfer the mixture to a blender and puree until smooth, adding reserved water as needed to reach your preferred consistency. Season with salt to taste.

For the meatballs, start by heating the sunflower oil in a small skillet over medium heat. Sauté the chopped garlic for 1 to 2 minutes until golden and fragrant, then set aside to cool.

In a food processor, combine the cooled garlic, beef, and ground white pepper. Process until finely minced. Add the egg, tapioca flour, and cold water, and continue blending until the mixture becomes smooth and paste-like.

Fill a medium saucepan halfway with water and bring it to a gentle simmer. To shape the meatballs, take a small portion of the meat mixture in one hand and gently squeeze it through your thumb and forefinger, forming a round ball roughly the size of a large grape. Scoop the ball using your other hand or a spoon, and drop it into the simmering water. Repeat until all the mixture is used. Cook the meatballs for 6 to 7 minutes, or until they float to the surface. Test one by slicing it in half to ensure it's fully cooked inside.

Transfer the cooked meatballs to the prepared broth, bring it to a gentle boil, then reduce to medium-low and simmer for another 10 minutes to allow the flavors to meld.

Prepare the noodles according to the package instructions. Once cooked, drain and transfer to a bowl of cold water to stop the cooking process. Drain again and set aside.

Add the chopped pak choy to the simmering broth and cook for about 45 seconds, just until tender but still vibrant. Remove using a slotted spoon and set aside.

To assemble, divide the noodles between serving bowls. Add a portion of pak choy and top with 3 to 4 beef meatballs. Ladle in a few generous spoonfuls of hot broth.

Finish each bowl with a dash of rice vinegar, tomato sauce, sweet soy sauce, light soy sauce, and a swirl of Sriracha. Garnish with crispy shallots and chopped celery leaves. Serve immediately, accompanied by the sambal for added heat and depth.