Rinse the shrimp paste. Place the shrimp paste in a strainer and carefully rinse with water to remove some of the excess salt. Drain well and set aside.

Render the pork fat. Heat a large pan over low to medium heat. Add the pork fat and 1/2 cup water. Cover and braise for about 5 minutes.

Reduce the heat to low and continue cooking for about 10 minutes, or until the pork fat becomes browned and most of the water has evaporated. Carefully remove the lid to avoid hot oil splatters.

Sauté the aromatics. Push the cooked pork fat to one side of the pan. Add the chopped onion and minced garlic to the rendered fat. Sauté until fragrant and softened.

Add the tomatoes. Add the minced tomatoes and stir together with the onion and garlic. Cover and cook for about 3 minutes, allowing the tomatoes to soften and release their juices.

Add the shrimp paste. Add the drained shrimp paste and stir thoroughly until it is well combined with the aromatics and pork fat.

Season. Add the ground black pepper, vinegar, and brown sugar. Stir well until the sugar dissolves into the mixture.

Add chili. If you prefer spicy bagoong, add the chopped chili and mix well.

Simmer. Cover the pan and simmer over low to medium heat for 15–20 minutes. Stir occasionally to prevent the mixture from sticking or burning.

Finish. Continue cooking until the bagoong becomes thicker and the sugar has caramelized slightly. Taste and adjust the sweetness, acidity, or seasoning according to your preference.

Cool and store. Turn off the heat and allow the bagoong to cool slightly before transferring it to a clean, airtight container.