Cheesy Beef Shepherd's Pie

Preheat the oven to a high temperature, specifically 350 degrees Fahrenheit or 175 degrees Celsius. To prevent sticking, lightly coat a 1 1/2-quart casserole dish with cooking spray.

Boil a large quantity of water in a substantial pot and add salt, covering the potatoes entirely. Bring the mixture to a rolling boil before reducing the heat to a low-medium setting and letting it simmer until the potatoes are tender, approximately 20 minutes. Remove from heat and let cool in a spacious container.

In the meantime, heat a large skillet over high heat. Combine ground beef and onion in the hot skillet, stirring constantly until the beef is broken down into small pieces, evenly browned, and no longer pink, roughly 10 minutes. Add green beans and condensed soup to the skillet, stirring until well combined.

Transfer the mixture from the skillet to the prepared casserole dish. To prepare, spread out a layer of cooked potatoes in a large bowl and add warm milk, beaten egg, garlic, pepper, and salt. Mash the potatoes until they form a smooth consistency.

Spread the mashed potato mixture evenly over the beef and green bean mixture in the casserole dish. Sprinkle a layer of Cheddar cheese on top.

Bake the dish in the preheated oven until the cheese is melted and the edges begin to brown, approximately 25 to 30 minutes.