How to Make It
Preheat the oven to 350°. On a work surface, using the flat side of a large knife, mash the garlic with 1 teaspoon of salt until a paste forms. Spread open the pork roast on the work surface and rub the inside with the garlic paste. Season the pork with pepper. Roll up the pork to form a neat roast and tie at 1-inch intervals. Season the outside of the roast with salt and pepper, then rub with the brown sugar.
In a large roasting pan, combine the sliced onions with the tomatoes and their juices, the ketchup, water and Tabasco. Set the pork roast on top of the sauce, cover with aluminum foil and bake for 2 hours. Increase the oven temperature to 450°, remove the foil and bake for 45 minutes longer, basting occasionally until the roast is nicely glazed. Transfer the roast to a carving board, cover loosely with foil and let rest for 10 minutes.
Meanwhile, pour the sauce into a large saucepan and simmer over moderately high heat, stirring occasionally, until thickened, about 12 minutes. Season with salt.
Untie the roast and slice it 1 inch thick. Serve with the sauce.