Preheat oven to 400 F. In a large saucepan, heat olive oil, cook onion and garlic until softened. Add in ground beef, breaking it up with a spatula until no longer pink. Drain grease and return to saucepan.
Add in ketchup, vegetables, beef broth, and flour. Continue to cook for a few more minutes, until the sauce has thickened. Spread mixture out in a large baking dish. Place potatoes in a large saucepan over meidum heat, cover with water and bring to a boil. Let cook until potatoes are fork tender. Drain and place into a large bowl.
Mash with butter, salt, and pepper. Spread mashed potatoes over meat mixture. Bake for 25-30 minutes.
