Preheat your oven to 350°F (175°C).
Cook the egg noodles according to package instructions until al dente.
In a skillet over medium heat, sauté the chopped onion until translucent.
Add the ground beef to the skillet, cooking until browned.
Drain any excess fat from the skillet and stir in the cream of mushroom soup and milk, mixing until combined.
Add the cooked egg noodles to the meat mixture, gently stirring to combine.
Season with salt and pepper to taste, then spread the mixture into a greased baking dish.
Top the casserole with shredded cheddar cheese.
Bake in the preheated oven for 25–30 minutes, or until bubbly and golden brown.
Let the casserole sit for a few minutes before serving.