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1
Place the oven rack to upper-middle of the oven, set a rimmed baking sheet on the rack, and preheat the oven to 400F (200C).
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2
With a sharp knife, cut 1/4 inch slits, spaced 1/2-inch apart, in the crosshatch patten on the surface of 8 mushrooms.
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3
Dice the remaining 2 mushroom caps and the reserved stems into 1/2-inch pieces, set aside.
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4
Brush both sides of the caps with 2 tablespoons of olive oil and sprinkle evenly 1 teaspoon salt over.
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5
Carefully transfer the caps, gill-side up, on the preheated baking sheet.
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6
Roast until the mushrooms have released some of their moisture and start to brown around the edges, about 10 minutes.
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7
Flip the caps over and keep roasting until the liquid has completely evaporated and the caps are golden brown, about 10 minutes longer.
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8
Remove the mushrooms from the oven and turn on the broiler.
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9
Meanwhile, add the spinach and water in a large skillet pan, cook the spinach until wilted, 2 to 3 minutes.
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10
Place the wilted spinach to colander set in the sink.
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11
With the back of a spatula, gently press the spinach to release excess water.
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12
Transfer the spinach to the cutting board and roughy chop.
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13
Return the spinach to the colander and press again.
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14
Set aside.
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15
Add the bread in a food processor, pulse until coarsely ground, and you should get about 1 1/2 cups of bread crumbs.
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16
Heat 1 tablespoon of olive oil and 1/2 tablespoon of butter in a 12-inch skillet over medium heat until the butter melts.
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17
Stir in the bread crumbs and salt to taste, cook, stirring constantly, until light golden brown, about 7 minutes.
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18
Transfer the crumbs to a small bowl and wipe out skillet with a paper towel.
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19
Return the cleaned skillet to medium-high heat, heat the remaining tablespoon of oil until hot.
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20
Stir in the chopped mushrooms and cook without stirring for 3 minutes.
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21
Keep cooking, stirring once a while, until lightly browned, about 5 minutes.
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22
Transfer to a medium bowl.
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23
Melt the remaining 1/2 tablespoon butter and the onions to skillet, cook, stirring, until the onions are light brown, about 6 minutes.
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24
Stir in the garlic and cook until fragrant, about 40 seconds.
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25
Stir in sherry and cook until almost all the liquid has evaporated, 1 to 2 minutes.
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26
Reduce heat to low and stir in reserved cooked mushrooms, spinach, thyme, goat cheese, cream, and walnuts.
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27
Keep cooking until the cheese has been melted and vegetables are well coated, about 2 minutes.
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28
Remove the pan from the heat, stir in lemon juice, and season with salt and black pepper to taste.
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29
Flip the caps, gill-side up, and distribute the filling evenly among mushrooms caps.
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30
Top each cap with 2 tablespoons of bread crumb mixture.
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31
Broil the mushrooms until the crumbs are golden brown, about 2 minutes.
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32
Serve.
