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1
Combine 1 1/2 cups hot water and porcini in small bowl.
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2
Let stand until mushrooms soften, about 30 minutes.
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3
Drain, reserving 2/3 cup soaking liquid.
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4
Chop porcini; set aside.
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5
Remove and chop stems from portobellos; place in large bowl.
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6
Using small spoon, scrape away dark gills from portobellos and discard.
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7
Cut portobello caps into 1/2-inch pieces; add to bowl.
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8
Heat 3 tablespoons olive oil in heavy large skillet over medium-high heat.
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9
Add chopped portobello stems and caps and saute 4 minutes.
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10
Stir in garlic and reserved porcini and saute until mushrooms are tender, about 10 minutes.
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11
Season with salt and pepper.
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12
Remove from heat.
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13
Preheat oven to 375F.
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14
Coat each of two 13x9x2-inch glass baking dishes with 1 tablespoon oil.
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15
Combine remaining 7 tablespoons oil, potatoes, parsley, thyme, rosemary, salt and pepper in large bowl; toss to coat.
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16
Layer 1/6 of potato mixture in each prepared dish (there will not be enough to overlap slices).
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17
Top potatoes in each with 1/4 of mushroom mixture.
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18
Repeat layering.
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19
Top with remaining potatoes.
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20
Pour 1/3 cup reserved porcini soaking liquid over potatoes in each dish.
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21
Cover dishes with foil.
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22
Bake gratins 45 minutes.
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23
Uncover and bake until tops are brown and potatoes are tender, about 40 minutes longer.
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24
(Can be prepared 2 hours ahead.
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25
Let stand at room temperature.
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26
Cover with foil and rewarm in 350F oven about 20 minutes.)
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27
*Dried porcini mushrooms are available at Italian markets, specialty foods stores and many supermarkets.
