Rinse the French roast and pat it dry. Season it generously with salt, pepper, and paprika.

Place the sugar in a sauté or braising pot. Over low heat, cook the sugar, stirring occasionally, until it melts and turns a caramel color.

Add the French roast to the pan on top of the caramelized sugar. Sear both sides of the meat two times, using tongs or a fork to rotate it, ensuring all surfaces are browned.

Once the meat is browned, lift it and place the sliced onions underneath it. Cover and cook over medium-low heat for 2.5 to 3 hours, making sure the flame is low enough to avoid burning the meat but high enough for the sauce to bubble slightly.

As the onions cook, their water will mix with the caramelized sugar, forming a sauce. In a small bowl, combine the potato starch and cold water, then add it to the sauce. Stir and cook until the sauce thickens.

Slice the French roast and serve it with the caramelized onion sauce.