Preheat Oven to 400 degrees

Heat olive oil in cast iron frying pan

Add onions, celery, and carrots to the frying pan and cook till fork tender this will take about 5 to 7 min.

Add ground beef and cook until browned.

Add the garlic, rosemary, thyme, salt and pepper. Cook for another 1 min until herbs become fragrant. Set aside in small bowl.

Combine tomato paste, flour, and Worcestershire sauce to pan and cook for 2 min until mixed.

Add ground beef mixture and beef broth to the base in the pan. Stir to combine and cook till gravy thickens

Pour into large oven safe dish and cover with mashed potatoes. for a crunchy golden brown layer on top of the potatoes brush with fresh butter.

Bake in 400 degree oven for 20 min or just until the potatoes begin to brown and let sit for 15 min prior to serving.