In a large sauté pan, melt the butter on low heat. When the butter is melted, add the onions and sauté on low to medium heat for about 2 minutes, or until translucent and soft. Season with salt and pepper. Turn heat down to low.
Gradually, stir in the flour to make a roux. Cook for about 1 minute and remove from the heat. Whisk in the milk to form a smooth sauce. Return to low to medium heat and cook until the sauce is thick and creamy. Season with salt, pepper, nutmeg, parsley, and sherry. Stir in the ham. Mix well and cook for 4 to 5 minutes on low heat. Pour the mixture into an 8 by 8½ inch baking pan and cool in the refrigerator so that the mixture will be easy to handle. Refrigerate for 2 to 3 hours or until well chilled. In a small mixing bowl, beat the eggs with water until frothy and pour into a medium bowl.
Combine the bread crumbs and flour in a second bowl. Season the mixture with salt and pepper.
Using your hands, shape the ham mixture into a log about ¾-inch thick. Using a knife, cut the logs into 1½ inch lengths. Dip the logs in the egg wash, letting the excess drip off. Roll the logs in the seasoned bread crumbs. Place the logs on a baking sheet and cover with plastic wrap. Refrigerate the logs for 2 to 3 hours.
Once you're ready to fry the croquetas, preheat the fryer. Fry croquetas in the hot oil, a few at a time, until golden brown, about 3 to 4 minutes. Remove croquetas from the oil and drain on a paper-lined plate. You can serve croquetas with a side of fresh lemon juice and parsley garnish.
• 4 tablespoons butter
• ½ cup finely minced onions
• ¼ cup plus 2 tablespoons flour
• 1½ cups milk
• black pepper
• ¼ teaspoon nutmeg
• 1 tablespoon finely chopped parsley
• 1 tablespoon dry sherry
• 12 ounces ground smoked ham (ready-to-eat or “deviled” ham)
• 2 eggs, mixed with 1 tablespoon water
• 1 cup bread crumbs
• vegetable oil for frying