Grease a 9x13 inch baking dish with cooking spray. Set aside.
Hit SAUTE on 6 quart Instant Pot, once it reads HOT, add butter and allow to melt.
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 any 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, corn, and about 4 oz shredded cheese, then taste and re-season, if desired.
Pour mixture into prepared dish and cover with foil to keep warm.
Clean Instant Pot thoroughly.
Make the Instant Pot Mashed Potatoes according to directions, then stir in 4 oz of shredded cheese.
Preheat oven to 450 degrees F, then remove foil from the dish and top evenly with mashed potatoes.
Sprinkle the top with remaining 8 oz cheese, then bake in preheated oven until the cheese has melted and the center is hot, about 10-15 minutes.
Serve and enjoy!