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1
Preheat oven to 450F.
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2
Wrap garlic cloves together tightly in foil.
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3
Trim beet stems to 1 inch if necessary and scrub beets.
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4
Wrap beets together tightly in foil.
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5
Roast garlic and beets in middle of oven until garlic is soft, about 30 minutes.
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6
Remove garlic from oven and continue to roast beets until very tender, about 45 minutes more.
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7
In a saucepan cover potatoes with cold salted water and simmer until tender, about 30 minutes.
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8
Drain potatoes and keep warm, covered.
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9
Unwrap garlic and peel skin from cloves, transferring garlic to a food processor.
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10
Unwrap beets carefully and, when cool enough to handle, slip off skins and stems and discard.
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11
Reserve 1 beet.
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12
Quarter remaining beets and add to processor.
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13
Peel and halve potatoes.
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14
Add potatoes to processor with vinegar and milk and pulse until mixture is just smooth (do not over-process or potatoes will become gluey).
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15
Transfer puree to cleaned saucepan and stir in lemon juice, 2 tablespoons water, and salt and pepper to taste.
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16
Heat puree over low heat, stirring, until hot.
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17
Stir in 2 tablespoons water and add enough remaining water to reach desired consistency.
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18
Cut reserved beet into 8 wedges and serve with puree.
