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1
Preheat the oven to 450 degrees F.
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2
Line a 9-by 13- by 2-inch pan or your oven's broiler pan with a sheet of heavy-duty aluminum foil large enough to fully wrap the roast.
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3
The shiny side of the foil should be up.
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4
Sprinkle the roast on all sides with salt and pepper and place it in the center of the foil.
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5
Spread the onion slices over the top of the roast and pour the vinegar around it.
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6
Bring the ends of the foil together and fold several times, and then fold the ends together to completely enclose the roast.
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7
Pour about 1 inch of water into the pan around the foil-wrapped roast.
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8
Bake until the meat is fork tender and brown, 3 to 4 hours.
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9
Check the water level in the pan regularly during cooking and replenish it if necessary.
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10
If any juice seeps from the foil seals during roasting, save it to use in making the gravy.
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11
When the roast is done, remove the package from the baking pan and let it cool for a few minutes.
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12
Open the package carefully to preserve all the juices and transfer the meat to a platter.
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13
Cover with a tent of foil to keep it warm while you make the gravy.
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14
Pour the roasting juices into a measuring cup and let the fat rise to the surface.
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15
Skim off the fat, reserving 4 tablespoons in a saucepan and discarding the rest.
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16
(If the fat measures less than 4 tablespoons, add enough butter to make up the difference.)
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17
Measure the remaining defatted pan juices and reserve.
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18
If you have less than 2 cups, add water to make 2 cups.
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19
Add the flour to the fat in the saucepan and stir with a wire whisk to make a roux.
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20
Cook over medium-low heat until the flour is lightly browned, about 1 minute.
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21
Slowly whisk in the reserved pan juices and stir until thickened.
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22
Slice the roast or cut it into chunks (it will be very tender), and serve it with the gravy.
