Preheat your oven to 400°F (200°C) and prepare a 9x13 inch baking dish by lightly greasing it with a little olive oil.
In a large skillet over medium heat, warm the olive oil. Add the diced onion and sauté for about 5 minutes until softened. Stir in the minced garlic and continue cooking for another 1 minute. Then, add the ground beef to the skillet, breaking it up with a spatula, and cook until browned through, around 7-10 minutes. Season with smoked paprika, thyme, salt, and pepper.
While the beef cooks, whisk together the Greek yogurt, cottage cheese, and cornstarch in a medium bowl until smooth and well-combined.
In the prepared baking dish, create a base layer by arranging half of the sliced potatoes evenly, followed by half of the cooked beef mixture. Pour half of the cheese mixture over this layer, then sprinkle with half of the cheddar cheese.
Repeat the layering process with the remaining potatoes, beef, cheese mixture, and top with the rest of the cheddar cheese.
Gently pour the beef broth around the edges of the casserole, making sure to distribute it evenly without disturbing the layers too much.
Cover the dish tightly with aluminum foil and bake for 40 minutes. Remove the foil and bake for another 20 minutes until the potatoes are tender and the cheese is bubbly and golden on top.
Allow the casserole to cool for about 10 minutes before serving. Garnish with fresh chives for a burst of color and flavor.