Preheat oven to 400 degrees F and grease a 9x13 inch baking dish with cooking spray. Set aside.
Melt butter in a large sauté pan.
Add in onion, carrots, garlic, beef, salt, pepper, rosemary, and thyme.
Cook, breaking up the beef as you go, until the meat is no longer pink and the vegetables are tender.
Drain off an excess grease.
Sprinkle the meat and veggie mixture with flour and cook, stirring constantly, for 1 minute.
Stir in the tomato paste, Worcestershire sauce, and broth.
Simmer, if necessary, to thicken.
Stir in peas and corn, then taste and re-season, if desired.
Pour mixture into the prepared dish and top evenly with mashed potatoes.
Bake for 25 minutes or until warmed through.
Serve and enjoy!
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