Preheat the oven to 450°F (230°C). Grease a 2‑quart gratin dish or an 8x8 baking dish.
Bring a large pot of salted water to a boil. Add the elbow macaroni and cook until just tender; do not overcook. Drain and rinse briefly with cool water to stop cooking and prevent sticking.
In a medium saucepan over medium heat, melt the butter. Whisk in the flour, salt, and black pepper to form a smooth paste (roux).
Slowly whisk in the milk, adding about 1/4 cup at a time, until fully incorporated. Continue cooking over medium heat, whisking frequently, until the sauce thickens and bubbles around the edges; do not boil.
Remove the saucepan from heat and stir in the shredded cheddar until melted and smooth. Stir in the Greek yogurt until the sauce is creamy.
Fold the cooked macaroni into the cheese sauce, making sure the pasta is evenly coated. Transfer the mixture to the prepared baking dish, scraping any remaining sauce into the dish.
Combine the breadcrumbs and smoked paprika, sprinkle evenly over the top of the macaroni, and bake at 450°F (230°C) for 15 minutes, until the topping is golden brown.
Remove from the oven and let sit a few minutes before serving. Serve hot.