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1
Preheat oven to 400F.
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2
If using fresh onions, bring a large pot of water to a boil.
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3
Add onions and cook 1 minute to loosen the skins.
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4
Drain.
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5
When cool enough to handle, trim both ends, leaving enough of the root end to keep the onions whole while roasting.
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6
Peel off the skins.
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7
Toss the prepared fresh onions (or frozen onions) with 1 tablespoon oil and 1/4 teaspoon salt in a large bowl.
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8
Spread in an even layer in a roasting pan large enough to accommodate all the onions in a single layer.
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9
(If youre using fresh onions, a 9-by-13-inch pan is large enough; if using frozen, you may need a larger pan.)
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10
Roast the onions, stirring occasionally, until soft and brown in spots, 45 minutes to 1 hour.
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11
Remove the roasting pan from the oven and add broth, stirring and scraping up any brown bits.
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12
Return the pan to the oven and roast for 10 minutes more.
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13
About 30 minutes after the onions start roasting, start the cream sauce.
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14
Melt butter with the remaining 2 tablespoons oil in a large saucepan over medium heat.
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15
Whisk in flour and cook, until the mixture bubbles and is free of lumps, about 30 seconds.
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16
Stir in milk, then add bay leaf, thyme, pepper and the remaining 3/4 teaspoon salt; bring to a gentle boil, whisking often.
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17
Reduce heat to the barest simmer and cook, whisking often, until the sauce has thickened to the consistency of thick gravy, about 5 minutes.
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18
Remove from the heat.
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19
Discard the bay leaf.
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20
Stir the roasted onions and any broth from the pan into the cream sauce.
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21
Stir in lemon juice.
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22
Transfer to a serving dish and serve warm.
