Fry the fish (see note 1 for alternative cooking method)
Pat-dry both sides of the milkfish with a kitchen towel. Season with salt and pepper.
Heat 1-inch deep vegetable oil in a skillet (stainless or non-stick) over high heat. When you see a wisp of smoke, it should be hot enough. Add bangus skin side down. Fry until crispy and brown. Cook the other side until brown but not toasted. Let it cool.
Using two forks, flake the fish into small or large pieces. You can exclude the skin or use it as a topping.
In a large bowl, toss the fish, half of the red onion, yellow onion, garlic, and chilies. Set aside until ready to serve.
Serve sisig (see note 4)
Heat vegetable oil in a sizzling plate/ cast iron pan or normal skillet over high heat. Add fish mixture followed by soy sauce, and liquid seasoning. Stir-fry for 1 to 2 minutes.
Add butter, calamansi juice, mayonnaise, and black pepper. Stir to combined. Taste and adjust seasoning as needed. Remove from heat.
Add egg, sprinkle remaining red onions. The residual heat will cook the egg while giving it a creamier texture. Serve and enjoy!
Notes
Milkfish - alternative cooking method is baking or air frying. Brush meat and skin with oil then season salt and pepper. Bake at 400f in a pre-heated oven for 30-45 minutes until brown. If using an air-fryer, cooking time should only take about 10-12 minutes,
Liquid seasoning - you can use Maggi, Knorr, or Braggs.
Calamansi – also known as calamondin. It can be substituted with lemon or lime but the flavor difference will be noticeable.