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1
Preheat oven to 350F.
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2
On a lightly floured surface, roll out dough 1/8 inch thick.
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3
Cut dough into 6 rectangles, 5 1/2 by 4 inches each.
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4
Fit dough into four 4 1/2-by-2 1/2-inch tart pans with removable bottoms, pressing into bottoms and up sides.
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5
Pierce bottoms of shells all over with a fork.
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6
Refrigerate or freeze until firm, about 30 minutes.
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7
Place shells on a rimmed baking sheet; bake until dry, 15 to 18 minutes.
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8
Transfer to a wire rack to cool completely.
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9
In a small saucepan, bring sugar, corn syrup, and water to a boil; wash down sides of pan with a pastry brush dipped in water to prevent crystals from forming.
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10
Reduce heat to low; cook, swirling pan to color evenly, until caramel is a rich amber color.
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11
Remove from heat; carefully add 1/4 cup cream (it will spatter), butter, creme fraiche, vanilla, and salt.
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12
Stir until smooth.
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13
Let cool slightly, 1 to 2 minutes; stir in nuts.
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14
Melt 5 ounces chocolate in a heatproof bowl set over (not in) a pan of simmering water (alternatively, you can melt in a microwave oven).
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15
Pour 1 1/2 tablespoons melted chocolate into each crust; with an offset spatula, spread to coat evenly.
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16
Refrigerate until set, about 10 minutes.
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17
Pour caramel mixture into each shell, dividing evenly.
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18
Bring 1/4 cup cream to a boil in a small saucepan.
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19
Pour over remaining 1 1/2 ounces chocolate in a heatproof bowl; whisk until smooth.
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20
Cool until slightly thickened, about 10 minutes.
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21
Pour about 1 tablespoon over caramel in 3 shells; smooth with an offset spatula.
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22
Store tartlets at room temperature, in an airtight container, up to 1 day.
