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1
Heat oven to 350.
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2
Slice mushrooms on a mandoline lengthwise, as thinly as is practical.
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3
Brush the inside of a 4 1/2-inch-by-8 1/2-inch nonstick loaf pan with some melted butter; line with parchment paper cut to fit the bottom of the pan.
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4
Layer the mushrooms in the pan, salting and spooning on a tablespoon or 2 of butter on each layer.
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5
Stack mushroom slices to about an inch above the pans top.
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6
Brush the inside of a piece of aluminum foil with melted butter, and wrap the mushrooms and the pan tightly.
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7
Place the loaf pan on a larger baking dish or rimmed sheet pan to catch any liquid that may bubble over.
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8
Place the pan in the preheated oven, and bake for 45 minutes to 1 hour, or until a skewer inserted in the mushrooms meets almost no resistance.
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9
Remove the aluminum foil, and continue to bake for 15 minutes, or until the top is browned.
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10
Remove the pan from the oven, and unwrap; pour off excess liquid.
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11
Place a piece of parchment paper and a second loaf pan on top, weighing it with cans of beans or bricks, at least 10 pounds of weight.
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12
Keep the outer baking dish underneath to collect overflow.
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13
Cool for 30 minutes, then refrigerate overnight.
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14
The next day, remove the loaf from the refrigerator, and take off the weights.
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15
Invert the loaf onto a rack lined with paper towels.
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16
You may have to break the butter seal with a knife so the mille-feuille releases, or even rub the bottom of the pan with a hot, wet cloth.
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17
Drain on the paper towels until ready to cook.
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18
Make the sauce: Cut the tomatoes into 2-to-3-inch wedges, and place in a blender.
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19
Blend on high speed until smooth; turn the blender to low, and slowly pour in the olive oil.
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20
Add salt, vinegar and sugar as needed.
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21
Do not strain.
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22
Transfer the loaf to a cutting board, and carefully slice 3/4-inch pieces with a serrated knife.
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23
Sear each piece in olive oil over medium heat in a heavy-bottomed saute pan.
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24
Cook until browned, about 2 minutes per side.
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25
Spoon some of the sauce onto each plate, and top with a slice of mushroom mille-feuille.
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26
Garnish with the herbs (if using sage or savory, fry it in olive oil).
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27
Sprinkle with salt, then serve.
