Hachis Parmentier is basically like a fancy shepherd's pie. Imagine you have some mashed potatoes and some ground beef with vegetables like carrots and onions. You put the ground beef and veggies in a dish, and then you cover it with the mashed potatoes like a blanket. Then you bake it all together in the oven until the mashed potatoes start to get a little brown on top. When it's all done, you have a warm and tasty meal that is comforting and filling. It's like having a big warm hug for dinner!