To begin, place the minced fish, salt, white pepper, grated garlic, and egg in a large bowl. Mix until smooth and sticky. Gradually add the cold water, stirring constantly. The texture should be tacky but not watery. Move to dough preparation.

Fold in tapioca flour with a spatula or your hands until a pliable dough forms. Do not over knead, as this can make the cakes tough. Continue until fully combined and smooth. Prepare for shaping.

Lightly oil your hands. Divide the dough into 8 equal parts. Flatten each piece, place a quarter of hard-boiled egg inside (if using), and fold the edges to seal. Shape into long oval cylinders or “submarine” form. Set aside.

Bring a pot of water to a gentle simmer. Add the pempek pieces and boil until they float, around 5–7 minutes. Do not let the water rapidly boil, or the texture may toughen. Remove and let them drain on a wire rack. Proceed to prepare the sauce.

Blend garlic and chillies into a paste. In a saucepan, combine the paste with water, palm sugar, tamarind water, vinegar, and salt. Simmer over medium heat for 10–15 minutes until slightly thickened. Strain if desired. Set aside to cool. Move to frying.

Heat oil in a pan over medium heat. Fry the boiled pempek until the surface is golden and crisp, about 2–3 minutes per side. Avoid overcrowding the pan to ensure even browning. Drain on paper towels. Prepare for serving.

Once slightly cooled, slice pempek diagonally into bite sized pieces. Arrange on a serving plate and prepare the accompaniments. Move to garnishing.

Serve the pempek with a generous pour of cuko sauce. You may garnish with sliced cucumber and sprinkle with fried shallots for freshness and crunch. For a spicier kick, add more chillies to the sauce as desired.