Preheat your oven to 375°F (190°C). Lightly grease a 2-quart white baking dish or a 9x9 inch casserole dish. Peel the potatoes and slice them into 1/8-inch thick rounds using a sharp knife or mandoline for even cooking.

In a large skillet over medium-high heat, cook the ground beef, breaking it up with a spoon, until no longer pink, about 5-7 minutes. Add the diced onion and cook for another 3-4 minutes until softened. Add the minced garlic and cook for 1 minute until fragrant. Drain any excess grease from the skillet.

Reduce the heat to low. To the skillet with the beef, add the cream of mushroom soup, milk, dried thyme, dried parsley, paprika, black pepper, and salt. Stir until everything is well combined and the sauce is smooth and heated through, about 2-3 minutes. Remove from heat.

Arrange half of the sliced potatoes in an even layer on the bottom of the prepared baking dish. Spoon half of the beef and sauce mixture evenly over the potatoes. Sprinkle with 1/2 cup of the shredded cheddar cheese. Repeat the layers with the remaining potatoes, the rest of the beef mixture, and another 1/2 cup of cheese.

Cover the dish tightly with aluminum foil. Bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the potatoes are fork-tender, the casserole is bubbly around the edges, and the cheese on top is melted and golden brown.

Remove the casserole from the oven and let it rest for 5-10 minutes. This allows the sauce to thicken slightly and makes serving easier. Garnish with fresh chopped parsley or chives if desired. Serve hot directly from the white baking dish.