In a large, oven proof skillet saute the beef on medium-high heat for 5 minutes, breaking it into pieces. Add the onions, carrots and celery and keep cooking for 10 more minutes.
Add salt, pepper, ketchup, dried herbs and 3 1/2 cups of beef broth. Stir, reduce heat to medium and cook for 20 minutes.
Add the peas, stir. Meanwhile, in a small dish, whisk the flour with the remaining 1/2 cup of beef broth. Add it to the beef, stir and cook for about 3 minutes, until the sauce starts to thicken.
Arrange scoops of mashed potatoes on top.
Bake at 400F for 25-30 minutes.