Preheat oven to 375 degrees. Place dough on a piece of parchment; roll out to 1/8 inch thick. Transfer to a baking sheet; chill 10 minutes. Remove from refrigerator; cut dough into four 3 3/4-by-5 1/2-inch rectangles. Fit dough into four 2-by-4-inch tart pans with removable bottoms, pressing into corners. Prick bottom of tarts all over with a fork. Chill at least 15 minutes.
Meanwhile, spread nuts in a single layer on a rimmed baking sheet; toast until golden and fragrant, about 10 minutes. Remove from oven; set aside.
Remove shells from refrigerator; line with parchment, pressing into edges. Fill with dried beans or pie weights. Place on a baking sheet; bake 20 minutes. Remove paper and beans; continue baking until crust is firm, 5 to 7 minutes. Transfer to a wire rack to cool completely.
Make caramel: In a small saucepan, bring sugar, corn syrup, and the water to a boil over medium-high heat; wash down sides of pan with a pastry brush dipped in water to prevent crystals from forming. Reduce heat to low; cook, swirling pan to color evenly, until caramel is a rich amber color. Remove from heat; carefully add 1/4 cup cream (it will spatter), butter, creme fraiche, vanilla, and salt. Stir until smooth. Let cool slightly; stir in nuts.
Melt 5 ounces chocolate in a heatproof bowl set over a pan of simmering water. Pour 1 1/2 tablespoons chocolate into each shell; spread to coat evenly. Chill until set, about 10 minutes. Remove from refrigerator; pour caramel into shell. Set aside.
Make ganache: Place remaining 3 ounces chocolate in a heatproof bowl.
Bring remaining 3/4 cup cream to a boil in a small saucepan. Pour over chocolate; whisk until smooth. Cool until slightly thickened, about 10 minutes. Pour 2 1/2 tablespoons over caramel; smooth with an offset spatula. Store at room temperature, in an airtight container, up to 1 day.
Vary them slightly by topping some with chocolate ganache and others with chocolate shavings. To make shavings: Chill leftover chocolate from step 5 until firm, about 15 minutes, then scrape with a knife or a dough scraper.