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1
Preheat the oven to 350 degrees F.
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2
Coarsely grate the cheese.
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3
Line a baking sheet with a silpat mat or parchment paper.
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4
Sprinkle 1 tablespoon of the cheese on the mat to make a thin disk, about 2 inches wide.
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5
Repeat with the remaining cheese, spacing the disks evenly on the pan to make 8 fricos.
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6
Bake rotating the pan once during baking, until the cheese melts together and is just golden, about 12 minutes.
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7
Cool fricos on the pan.
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8
Position a rack 6 inches from the broiler and preheat.
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9
Slice the mushrooms as thin as possible.
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10
Toss with the lemon juice and season with the salt and pepper, to taste.
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11
Brush the chicken breast with olive oil and mustard.
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12
Season with the salt and pepper.
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13
Place the chicken in a gratin or casserole dish and broil, turning as needed until an instant-read thermometer inserted into the breasts registers 160 degrees F, about 25 minutes.
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14
Transfer the chicken to a plate, reserve the pan.
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15
Add the broth to the pan, and stir with a wooden spoon to release the brown bits that cling to the pan.
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16
Reserve the pan drippings.
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17
Whisk the balsamic vinegar, salt, and pepper, to taste, in a large bowl.
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18
Gradually whisk in the oil, and the pan drippings starting with a few drops and then adding the rest in a steady stream, to make a dressing.
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19
Slice the chicken.
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20
Toss the spinach and mushrooms with the dressing and divide among 4 plates.
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21
Scatter the chicken over the salads, top with the fricos and serve.
