Finely chop the sweet Spanish onion.

Sauté the chopped onion in margarine until it becomes tender.

Thaw the frozen hash browns.

In a large bowl, combine the sautéed onion, thawed hash browns, and grated Swiss cheese.

Add salt and pepper to taste.

Mix the ingredients thoroughly.

Spoon the mixture into a 13 x 9-inch baking dish.

In a separate bowl, beat the eggs.

Add milk to the beaten eggs and mix well.

Pour the egg and milk mixture over the casserole in the baking dish.

Bake at 350°F (175°C) for 20 to 30 minutes, or until the top is browned.

Allow the casserole to cool for 5 minutes before serving.