In a pan (cast iron is best) melt your butter and then add your diced onions. Cook until softened.
Sprinkle in and whisk the flour into your mixture. Add onion powder and garlic powder. Stir until bubbly and smooth. Slowly add the beef broth and whisk together until smooth. (if you want to add diced mushrooms add now)
Add the tomato paste, Worcestershire sauce, and Dijon mustard. Start to combine and cook until the gravy reaches your desired thickness.
Taste, add salt and pepper to taste. Pour over prepared meatloaf.