In a large bowl, combine ground meats, panko, eggs, melted butter and seasonings. Roll mixture into balls.
In a skillet on medium-high heat, cook meatballs in olive oil, until browned on all sides. Transfer to a paper towel-lined tray and set aside.
Prepare the gravy. In the same skillet, melt butter and whisk in the flour until lightly browned. Slowly pour in the beef broth while whisking continuously. Keep whisking and cooking until slightly thickened. Stir in the heavy cream and season with salt and pepper.
Place meatballs in the gravy and simmer for about 3 to 4 minutes.
Cook egg noodles to al dente and drain. In a baking dish, mix noodles together with meatballs and gravy. Sprinkle with shredded Gruyere cheese.
Bake at 375 degrees F until slightly golden and bubbling. Garnish with chopped chives or parsley.