Dice the pork fat and mix it with the ground beef and ground pork. Add 1 tablespoon oyster sauce, 1/2 tablespoon fish sauce, 1 scant tablespoon cornstarch, 1/2 teaspoon black pepper, and finely chopped onion. Mix everything well.

Peel and finely chop the garlic. Sauté the garlic until fragrant but not browned, let it cool, then add it to the meat mixture. Mix well and let it marinate for 15 minutes.

Wash the betel leaves and pat them dry. Wrap the meat mixture in the betel leaves to form rolls, then pan-fry until cooked through. Alternatively, spray with oil and air-fry until done.

Once cooked, transfer the betel leaf rolls to a plate and serve.