Preheat the oven to 375°F (190°C).
In a large skillet over medium heat, heat 1 tablespoon olive oil. Add the chopped onion and cook until translucent, about 5 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground beef to the skillet. Cook, breaking it up with a spoon, until browned and cooked through, about 7-8 minutes.
Season the beef mixture with salt, black pepper, dried thyme, and paprika. Stir well and remove from heat.
In a small saucepan, heat the remaining 1 tablespoon olive oil over medium heat. Stir in the flour and cook for 1 minute to form a roux.
Gradually whisk in the beef broth and milk, stirring constantly until the sauce thickens, about 3-4 minutes. Remove from heat.
Lightly grease a 9×13 inch baking dish. Spread half of the sliced potatoes evenly on the bottom of the dish.
Layer half of the ground beef mixture over the potatoes.
Pour half of the thickened sauce evenly over the beef layer.
Repeat the layers with the remaining potatoes, ground beef, and sauce.
Cover the casserole with aluminum foil and bake in the preheated oven for 45 minutes.
Remove the foil, sprinkle the shredded cheddar cheese evenly on top, and bake uncovered for an additional 15 minutes or until the cheese is melted and bubbly and the potatoes are tender.
Remove from the oven and let the casserole rest for 10 minutes before serving.