Preheat oven to 375°F (190°C). Butter a 9x13 inch baking dish. In a medium saucepan, melt 3 tablespoons of butter over medium heat. Whisk in the flour and cook for 1 minute until golden. Gradually whisk in the milk and chicken broth until smooth. Bring to a simmer, stirring constantly until the sauce thickens. Remove from heat and stir in the cheddar cheese, Parmesan, garlic powder, onion powder, paprika, salt, and pepper.

Arrange half of the potato slices in the prepared baking dish, overlapping slightly. Top with half of the onion slices and pour half of the cheese sauce over the potatoes. Repeat with remaining potatoes, onions, and sauce. Cover with foil and bake for 45 minutes.

While potatoes bake, season beef chops with thyme, rosemary, garlic powder, salt, and pepper. Heat olive oil in a large skillet over medium-high heat. Sear the chops for 3-4 minutes per side until golden brown. Remove chops and set aside.

In the same skillet, melt 2 tablespoons of butter. Add beef broth and bring to a simmer. Whisk in the cornstarch mixture and cook until the gravy thickens, about 2-3 minutes.

Remove potatoes from oven and uncover. Arrange the seared beef chops on top of the potatoes. Pour the gravy over the chops. Return to oven uncovered and bake for another 20-25 minutes, until potatoes are tender and chops are cooked through.