Before starting, preheat broiler to high and wash and dry all produce. Peel, then cut potatoes into ½-inch pieces. Combine potatoes, 1 tsp salt and enough water to cover (approx. 1 inch) in a large pot. (NOTE: Use same for 4 ppl.) Cover and bring to a boil over high heat. Once boiling, reduce the heat to medium. Simmer, uncovered, until the potatoes are fork-tender, 10-12 min.
While potatoes cook, strip 1 tbsp thyme leaves (dbl for 4 ppl) from stems. Peel, then mince or grate garlic.
Heat a large oven-proof pan over medium heat. When hot add 1 tsp oil (dbl for 4 ppl), then beef. Cook, breaking up beef into smaller pieces, until no pink remains, 4-5 min.** Season with salt and pepper. Transfer to a plate and set aside. Heat the same pan over medium heat. When hot, add 1 tbsp butter (dbl for 4 ppl), then mirepoix, thyme and garlic. Cook, stirring often, until veggies soften slightly, 3-4 min.
Add beef and any juices (from the plate) to the pan. Add tomato sauce and sprinkle with flour. Cook, stirring often, until veggies and beef are coated, 1-2 min. Add peas, soy sauce and ¾ cup water (dbl for 4 ppl). Bring to a boil over high heat. Reduce heat to medium and cook, stirring often, until sauce thickens and veggies are tender, 4-6 min. Season with salt and pepper.
When the potatoes are tender, drain and return to the same pot. Add cream cheese, cheddar, ¼ cup milk and 1 tbsp butter (dbl both for 4 ppl). Using a potato masher, mash together until creamy. Season with salt and pepper. (NOTE: If you don't have an oven-proof pan, transfer beef and veggie mixture to a 8x8-inch baking dish for 2 ppl or a 9x13-inch dish for 4 ppl.)
When beef and veggies are done, top with mashed potatoes, spreading evenly over top. Broil in the middle of the oven until potato topping begins to brown, 4-5 min. Remove cottage pie from the oven and let stand for 5 min. Divide cottage pie between plates.