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1
Cut off the stem and root ends of the onions, then halve them lengthwise and peel away the dried brown skin.
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2
Cut the onions lengthwise into one-fourth-inch-thick slices.
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3
As you finish, gather the onions in a large, heavy-bottomed pot (preferably cast iron).
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4
A 7-quart pot will work just about perfectly.
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5
When all the onions have been sliced, pour over the vegetable oil and the salt and stir to combine.
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6
Set over medium heat and cover.
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7
Cook until the onions begin to wilt, stirring every 10 to 15 minutes to keep from sticking.
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8
As the onions soften, they will reduce in size quite dramatically.
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9
After about 25 minutes, the onions will be quite soft and will begin to stick to the bottom.
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10
Reduce the heat to low and continue cooking with the pot covered, stirring every 10 to 15 minutes to keep from sticking.
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11
After about 50 minutes, the onions will be silky and will be swimming in moisture.
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12
Remove the lid and increase the heat back to medium.
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13
Cook, stirring frequently, until the moisture has mostly evaporated and the onions have begun to turn golden, about 30 more minutes.
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14
Once again, reduce the heat to low and continue cooking, stirring every 15 to 20 minutes, until the onions really begin to brown more deeply, about 2 more hours (this will make 2 1/2 to 3 hours total).
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15
At this point, you'll need to watch the onions very carefully, stirring every couple of minutes or so.
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16
Cook until the onions have been reduced to a deep, reddish-brown marmalade, watching that they do not dry out, about 1 more hour, 3 to 4 hours total.
