In a mixing bowl, combine the ground beef, brown sugar, soy sauce, and salt. Stir well until the seasonings are evenly distributed throughout the meat. Add the finely chopped onion, minced garlic, red pepper flakes, and black pepper, blending thoroughly to create a cohesive mixture. The texture should be sticky and well-bound, ensuring the flavors are evenly incorporated.

Prepare 12 square sheets of wax paper. On a clean surface or cutting board, lay down one sheet and spoon about 2 tablespoons of the beef mixture onto the lower half of the paper. Shape the meat into a small log, roughly 3 to 4 inches long. Fold the wax paper over the mixture, pressing the beef gently with your thumbs to form a tight roll. Continue rolling until sealed. Repeat the process with the remaining mixture and sheets of wax paper.

Once all are shaped, place the wrapped longganisa logs on a tray and refrigerate overnight. This chilling process helps the flavors develop and allows the meat to firm up, making it easier to cook.

When ready to cook, heat a thin layer of oil in a nonstick skillet over medium heat. Unwrap each longganisa and place them carefully in the hot oil. Fry slowly, turning occasionally to brown all sides evenly. Continue cooking until the sausages are caramelized on the outside and cooked through to the center, about 8 to 10 minutes depending on thickness.

Transfer to a serving plate and drain excess oil on paper towels if needed. Serve hot alongside garlic fried rice and sunny-side-up eggs for a classic Filipino breakfast experience.