Preheat the oven to 450°F (230°C).
Bring a large pot of salted water to a boil and cook 1 pound elbow macaroni until just tender; do not overcook. Drain in a colander and rinse briefly with cool water to prevent sticking.
In a medium saucepan over medium heat, melt 2 tablespoons unsalted butter. Whisk in 2 tablespoons flour, 1 1/4 teaspoons salt, and 1/4 teaspoon black pepper to form a paste and cook 1 minute, stirring.
Slowly whisk in 2 cups low-fat milk, about 1/4 cup at a time, until smooth. Continue cooking over medium heat, whisking frequently, until the sauce thickens and bubbles around the edges; do not boil.
Remove the sauce from heat and whisk in 1 1/2 cups shredded sharp cheddar until melted, then stir in 3/4 cup Greek yogurt until smooth.
Toss the drained macaroni into the cheese sauce, making sure the pasta is evenly coated.
Scrape the macaroni and cheese into a greased 2‑quart gratin dish or 8×8 baking dish and spread into an even layer.
Mix 2 tablespoons breadcrumbs with 1/8 teaspoon smoked paprika and sprinkle evenly over the pasta.
Bake in the preheated oven for 15 minutes, until the top and breadcrumbs are golden brown to your liking. Serve hot.