A hard-boiled egg is a simple and nutritious food made by cooking an egg in its shell until both the white and yolk are firm. To make one, you place the egg in a pot of water, bring it to a boil, and then let it simmer for about 9 to 12 minutes. After cooking, the egg is cooled in cold water, making it easier to peel. Hard-boiled eggs are versatile and can be enjoyed on their own, sliced in salads, or used in dishes like deviled eggs. They are a great source of protein and can be a healthy snack or part of a meal.