Preheat the oven to 400°F (200°C).

Trim excess fat from the roast, leaving about 1/4 inch fat. Liberally season all sides of the roast with salt, pepper, and garlic powder.

Place the roast, fat-side up, in a Dutch oven and add the onions around and on top of the roast.

Cover and bake in the oven for 1 1/2 hours until aromatic.

Reduce the heat to 350°F (175°C) and continue baking, turning the meat every 30 minutes and keeping it covered, for an additional 3 hours or until the roast is browned and the internal temperature reaches 145°F (65°C).

Check the tenderness of the roast with a fork. If not tender enough, add additional cook time in 30-minute increments until the meat easily falls apart.

Remove the roast from the oven and transfer it to a cutting board. Tent with foil and let it rest for at least 20 minutes.

Meanwhile, whisk together the water and flour in a small bowl.

Place the Dutch oven on the stovetop over medium heat. Smash the remaining onion pieces and stir carefully to avoid burning the gravy. Slowly add the water-flour mixture while whisking until the desired gravy thickness is achieved.