- Preheat oven to 375 F degrees.  Heat a BIG oven safe skillet over MED heat.  Add oil and ground beef and cook about 4 minutes, or until cooked through, breaking it up into small crumbles as it cooks.  Once browned, transfer to a plate.  If needed, drain excess grease before adding the beef to a plate.   
- Add butter to same skillet.  Once melted, add onion, carrots, mushrooms, garlic, dried oregano, and 1/2 the salt.  Cook, stirring occasionally, about 8-10 minutes.   
- Add in tomato paste, stirring to combine, and cook 5-7 minutes, until tomato paste is a dark, brick red color (this really brings out the tomato flavor).   
- Return cooked ground beef to the skillet, then stir in beef stock, Worcestershire sauce remaining salt, and black pepper.  Simmer for a few minutes, until mixture is slightly thickened. 
- Top with mashed potatoes (see recipe notes section), and Parmesan cheese.  Use a fork to rough up the top of the potatoes, then dot with the butter pieces. 
- Bake 40-45 minutes, until bubbly and potatoes are browned.  Let cool 5-10 minutes before serving.  Sprinkle with minced fresh parsley and enjoy!