Turn on the broiler to high.
Dry and wash the produce.
Cut potatoes into pieces measuring 12 inches long.
Pluck thyme leaves from stems; roughly chop leaves. Slice 14-inch-thick half moons from carrots, after trimming, peeling, and halving them lengthwise.
Prepare celery by dicing it finely. Prepare the onion by halving, peeling, and chopping it finely.
Make sure the potatoes are covered by 2 inches of salted water in a medium pot. Boil until tender, about 15-20 minutes.
Return potatoes to pot after draining.
Add sour cream, thyme, butter, and a sprinkle of water if necessary to make potatoes smooth and creamy. Sprinkle generously with salt and pepper.
Remove from heat and cover until ready to serve.
In a medium, ovenproof pan (use a large pan for four servings) heat a drizzle of oil over medium-high heat while the potatoes are cooking.
Toss the carrot in the pan with the salt and pepper. Cook for 2-3 minutes, stirring occasionally.
Season with salt and pepper after adding celery, onion, and a large drizzle of oil.
Stir continuously for 5-7 minutes until the vegetables are just tender.
Add a splash of water if vegetables are browning too quickly.
Cook for 30 seconds with 2 tsp of chopped thyme and garlic powder.
Sprinkle salt and pepper over the beef and veggies as you cook.
Breaking up the meat into pieces, cook until browned and cooked through, 4-6 minutes.
Add the flour and stir until thoroughly combined.
Add half the crushed tomatoes (all for 4 servings) and ½ cup water (¾ cup for 4) to the pan with the beef mixture.
Taste and season with salt and pepper.
TIP: If your pan isn’t ovenproof, transfer the mixture now to a baking dish.
Top beef filling with an even layer of mashed potatoes, leaving a gap around the edge of pan.
Evenly sprinkle with cheddar.
Broil until browned, 3-4 minutes. TIP: Watch carefully to avoid burning. Serve directly from the pan.