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1
Heat the oven to 350 degrees F and arrange a rack in the middle.
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2
Line a rimmed baking sheet with 2 overlapping pieces of aluminum foil that wrap over the edges of the baking sheet.
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3
Arrange the matzo in a single layer on the baking sheet, breaking pieces as needed to fill any empty spaces; set aside.
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4
Place the butter, brown sugar, and 3/4 teaspoon of the fleur de sel in a small saucepan over medium heat and stir with a rubber spatula until the mixture comes to a boil, about 5 minutes.
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5
Continue to boil, stirring occasionally, for 3 minutes more.
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6
Remove from the heat, add the vanilla (pour it in slowly, as the mixture may bubble up), and stir to combine.
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7
Pour the caramel over the matzo and spread it evenly using the rubber spatula.
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8
Place the baking sheet in the oven (use care because the baking sheet may be hot from the caramel) and bake the matzo until small bubbles cover the surface and the caramel is fragrant (do not let the caramel burn), about 10 minutes.
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9
Remove from the oven, sprinkle with the chocolate chips, and set aside until the chips have softened, about 5 minutes.
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10
Using a rubber spatula, spread the chocolate over the caramel.
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11
Sprinkle with the nuts and remaining 3/4 teaspoon fleur de sel.
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12
Refrigerate the brittle until cool, about 15 minutes.
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13
Break into pieces and serve.
