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1
Place the dried porcinis in a bowl or a pyrex measuring cup and pour on 1 1/2 cups boiling water.
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2
Soak for 30 minutes.
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3
Line a strainer with cheesecloth and place over a bowl.
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4
Drain mushrooms, then squeeze in cheesecloth to extract juices.
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5
Rinse several times and chop medium-fine.
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6
Measure out 1 cup of broth.
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7
Meanwhile heat oven to 375 degrees.
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8
Rub inside of a 3-quart gratin dish or baking dish all over with the cut half garlic clove and lightly oil with olive oil.
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9
Heat oil in a wide, heavy nonstick skillet over medium heat.
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10
Add onion or shallots and cook gently until just tender, 3 to 5 minutes.
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11
Turn up heat to high and add mushrooms.
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12
Cook, stirring, until they begin to sweat, 2-3 minutes, reduce heat to medium, and add minced garlic, thyme, rosemary or sage and dried porcinis.
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13
Cook, stirring, until fragrant, about 30 seconds.
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14
Season mushrooms with salt and pepper and continue to cook over medium heat until soft, about 5 more minutes.
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15
Add wine and cook, stirring, until it is no longer visible in the pan.
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16
Taste and adjust seasoning.
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17
In a large bowl combine potatoes, mushrooms, half the cheese, and salt and pepper.
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18
Arrange in an even layer in gratin dish.
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19
Combine milk and mushroom broth.
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20
Season generously with salt and pour over the potatoes and mushrooms.
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21
Press the vegetables down into the liquid.
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22
Bake 1 hour.
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23
Every 20 minutes remove gratin dish and press potatoes and mushrooms down into the liquid with the back of a large spoon.
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24
After 1 hour, sprinkle on remaining cheese and bake for another 30 minutes, until top is golden and the sides crusty.
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25
Remove from the oven and allow to sit for 10 to 15 minutes before serving.
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26
Serve hot or warm.
