In a saucepan, melt 1/4 cup butter. Sauté onions, hotdogs, bell peppers and mushrooms. Cook for 5 minutes over moderate heat. Transfer mixture in a bowl and set aside.
Using the same pan, melt 1/4 cup butter. Add flour and whisk together to form a roux. Slowly pour in beef broth while mixing. Add milk and continue to cook, stirring constantly over moderate heat. Continue to cook until sauce is slightly thick. Add cooked hotdog-vegetable mixture and mix well. Season with salt and pepper. Remove from heat and pour sauce on top of cooked pasta. Top with grated cheese.