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1
Peel and thinly slice all of the onions into half moons.
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2
Transfer all the onions to the slow cooker the slow cooker should be half to three-quarters full.
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3
Drizzle the olive oil or melted butter and the salt, if using, over the top of the onions.
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4
Toss to evenly coat all the onions with a thin glaze of oil.
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5
Cover the slow cooker and cook for 10 hours on LOW.
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6
If you're around while the onions are cooking, stir them occasionally this will help them cook more evenly, but isn't strictly necessary.
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7
After 10 hours, the onions will be golden-brown and soft, and they will have released a lot of liquid.
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8
If you like them as they are now, stop cooking and pack them up.
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9
Optional cook an additional 3 to 5 hours with the lid ajar: If you'd like jammier, more concentrated onions with a deeper color, continue cooking for another 3 to 5 hours on LOW.
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10
Leave the lid ajar so the liquid can evaporate.
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11
Check every hour and stop cooking whenever the onions look and taste good to you.
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12
Remove the onions with a slotted spoon and transfer them to refrigerator or freezer containers.
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13
If any liquid remains in the slow cooker, transfer the liquid to a separate container this can be used as cooking broth in another recipe.
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14
Onions will keep in the refrigerator for one week or in the freezer for at least 3 months.
