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1
Adjust oven rack to middle position and heat oven to 350 degrees F. Place a rack over a rimmed baking sheet.
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2
Set aside.
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3
Pat the steaks dry with paper towels and season on both sides with salt and pepper.
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4
Heat the oil in a large skillet over medium-high heat just until smoking.
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5
Place the steaks in the skillet and cook to sear, about 3 minutes.
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6
Flip to sear the other side, about 3 minutes.
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7
Transfer the steaks to the prepared rack and roast in the middle of the oven until the steaks are medium rare (an instant-read thermometer inserted into the center of the steaks will register 125 degrees F), about 12 minutes.
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8
Meanwhile, once you have transferred the steaks to the oven, immediately add the mushrooms to the skillet and season with salt and pepper.
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9
Reduce the heat to medium low and cook, stirring occasionally, until golden brown, 8 to 10 minutes.
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10
Add parsley and toss to combine.
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11
Taste and adjust the seasoning with salt and pepper.
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12
Keep warm.
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13
Transfer the steaks to a warmed serving platter, tent with foil, and let rest for 10 minutes.
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14
Remove any fat on the edges and cut the steaks into 1/2-inch-thick slices.
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15
Serve topped with mushrooms and with the spinach on the side.
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16
Melt the butter over medium-low heat in a medium saucepan.
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17
Add the shallot and cook until translucent, 2 to 3 minutes.
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18
Increase the heat to medium.
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19
Whisk in the flour and cook until foaming but not browned, about 1 minute.
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20
Whisk in the milk.
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21
Add the cayenne and nutmeg and season with salt and pepper.
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22
Bring to a boil; continue cooking, stirring constantly, until the sauce thickens, about 2 minutes.
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23
Add the spinach and stir to combine.
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24
Cook until heated through, 3 to 5 minutes.
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25
Taste and adjust the seasoning with more salt and pepper if needed.
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26
Serve immediately.
