Step 1

Preheat the oven to 400 degrees F (200 degrees C).

Step 2

Trim excess fat from roast, leaving about 1/4 inch fat. Liberally season all sides with salt, pepper, and garlic powder. Place roast, fat-side up, in a Dutch oven. Place onions on and around the roast.

Step 3

Cover and bake until aromatic, about 1 1/2 hours. Reduce heat to 350 degrees F (175 degrees C) and continue to bake, turning the meat every 30 minutes and keeping covered, until roast is browned and cooked through, about 3 hours more. An instant-read thermometer inserted in the thickest part of the roast should read 145 degrees F (65 degrees C).

Step 4

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

Step 5

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

Step 6

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

Step 7

Place the Dutch oven, uncovered, on the stovetop over medium heat. Smash the remaining onion pieces and stir, being careful not to let the gravy burn. Slowly add water-flour mixture, whisking until cooked through and desired thickness is achieved.

Step 8

Slice roast and serve alongside gravy.