Preheat oven to 375°F (190°C) and grease a 9x13 inch baking dish.
In a large skillet over medium-high heat, brown the ground beef with diced onions until meat is cooked through and onions are translucent. Drain excess fat.
Stir in minced garlic, thyme, salt, and pepper to the beef mixture; cook for 1 minute then set aside.
In a small saucepan, melt butter over medium heat. Whisk in flour and cook for 2 minutes to create a roux.
Slowly whisk in milk and cook until the sauce thickens. Remove from heat and stir in 1 cup of cheddar cheese until melted.
Layer half of the sliced potatoes in the prepared baking dish. Top with the ground beef mixture.
Layer the remaining potatoes over the beef. Pour the cheese sauce evenly over the top.
Cover with foil and bake for 45 minutes.
Remove foil, sprinkle with the remaining 1 cup of cheddar cheese and paprika.
Bake uncovered for an additional 15 minutes or until potatoes are tender and top is golden brown.