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1
Preheat oven to 450 degrees F.
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2
Remove white papery skins from garlic heads (do not peel or separate cloves).
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3
Place the heads on a sheet pan, covered with foil and drizzle with olive oil.
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4
Bake for 40 to 50 minutes; cool 10 minutes.
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5
Separate cloves; squeeze to extract garlic pulp (you should have about 1/4 cup).
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6
Discard skins.
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7
Preheat oven to 375 degrees F.
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8
Heat oil in a large nonstick skillet over medium-high heat.
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9
Add shallots; saute 3 minutes or until softened.
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10
Add mushrooms; saute 5 minutes.
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11
Stir in vinegar; cook 1 minute or until liquid almost evaporates.
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12
Remove from heat.
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13
Place cream, garlic pulp, flour, thyme, salt, and pepper in a food processor; process until smooth.
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14
Arrange one-third of potatoes in a 13 x 9-inch baking dish coated with cooking spray.
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15
Spread half of the shallot/mushroom mixture over potatoes.
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16
Repeat procedure with remaining potato slices and shallot mixture, ending with potato slices.
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17
Pour cream mixture evenly over potatoes.
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18
Cover the baking dish and bake for 30 minutes.
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19
Remove foil; bake, uncovered, 30 minutes.
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20
Sprinkle with cheese; bake 15 minutes or until cheese is golden.
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21
Test for doneness by sticking a fork into the casserole.
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22
It should sink through easily.
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23
Let stand 10 minutes before serving.
