First, clean your fresh fish thoroughly and remove all bones (Linisin at tanggalin lahat ng tinik ng isda). Cut the fish into small chunks and keep them very cold, below 40°F/4°C (Putulin ng maliliit at panatilihing malamig).
Place the cold fish chunks into your food processor and grind until it becomes a smooth paste (Gilingin ang isda hanggang maging paste). Transfer the fish paste to a large mixing bowl.
Add 2 tablespoons cornstarch, 2 teaspoons salt (asin), 1 teaspoon sugar (asukal), and ¼ cup ice-cold water (malamig na tubig) to the fish paste. Mix these ingredients together until well combined (Haluing mabuti).
Now comes the important traditional pounding technique. Lift the mixture and forcefully slam it back into the bowl. Continue this pounding motion for about 15 minutes or approximately 100 times. The mixture will become smooth and glossy (makintab) and should pull away cleanly from the sides of the bowl. Keep the mixture cold throughout this process, ideally below 50°F/10°C.
While pounding the fish paste, prepare the sauce (Ihanda ang sawsawan). In a pot, combine 2 cups water (tubig), ⅓ cup soy sauce (toyo), 1 minced head of garlic (tinadtad na bawang), 3 finely chopped shallots (sibuyas tagalog), 4 chopped Thai chilies (siling labuyo), 1 cup brown sugar (asukal na pula), 1 tablespoon all-purpose flour (harina), 1 tablespoon cornstarch, 1 teaspoon salt (asin), and ½ teaspoon ground black pepper (paminta).
Heat the sauce mixture to 200°F/93°C while stirring constantly (Pakuluan habang hinahalo). Simmer for 3-5 minutes until it thickens. Remove from heat and let it cool to room temperature.
Return to your fish paste mixture. Wet your hands with cold water and shape the mixture into 1-inch balls (Gumawa ng maliliit na bola). Place the shaped balls on a clean plate.
Bring a pot of water to exactly 175°F/80°C. Carefully drop the fish balls into the hot water and cook until they float to the surface, about 1-2 minutes (Lutuin hanggang lumutang). Remove them with a strainer and let them cool completely.
Heat cooking oil in a deep pan to 350°F/175°C. Fry the cooled fish balls in small batches, 8-10 pieces at a time, until golden brown (Prituhan hanggang maging golden brown). Don't overcrowd the pan (Huwag masyadong marami sa kawali). Remove and drain on paper towels.
If you want extra crispy fish balls, you can double-fry them. After the first frying, let them cool for 2 minutes, then fry again at 350°F/175°C for 30 seconds.
Serve immediately while hot and crispy (Ihain habang mainit), with the prepared sauce on the side for dipping. For the authentic street food experience, serve them skewered on bamboo sticks (Tusukan ng stick).
To store uncooked fish balls, keep them in an airtight container in the refrigerator at 40°F/4°C for up to 3 days, or freeze at -0°F/-18°C for up to 3 months (Ilagay sa malamig). Store the sauce separately in the refrigerator. Always bring frozen fish balls to room temperature before cooking.
If your mixture is too soft, add cornstarch one teaspoon at a time. If the fish balls aren't bouncy enough, they need more pounding. If they break apart while cooking, either the water is too hot or the mixture is too loose. If they don't float while boiling, increase the water temperature to 175°F/80°C.