If using taro leaves, remove the tough stems and veins. Rinse the leaves thoroughly and pat dry.
If using spinach, rinse and pat dry the leaves.
In a mixing bowl, combine the coconut milk, chopped onion, minced garlic, diced tomato, and corned beef (if using).
Season with salt and black pepper to taste. Mix well.
Take a banana leaf or a piece of aluminum foil and place a few taro or spinach leaves in the center.
Spoon some of the coconut milk mixture onto the leaves.
Fold the leaves over the filling to create a small parcel. If using banana leaves, secure the parcel with kitchen twine or toothpicks. If using aluminum foil, wrap tightly to seal.
Preheat your oven to 350°F (175°C) or prepare a steamer.
Place the wrapped parcels in a baking dish if using the oven, or directly in the steamer basket if steaming.
If baking, cook for about 1 hour. If steaming, steam for about 1 hour as well.
Carefully unwrap the parcels and transfer the palusami to a serving dish.
Enjoy your meal!