Gluten-Free Dark Chocolate Caramel Tart with Sea Salt

I found the base recipe for this decadent tart over a year ago in Saveur Magazine. I had always intended to make it, but never had a reason (or a tart pan). After realizing this would be the perfect dessert for a coworker's birthday, I was commissioned to make two more for another event, and made this last one for a wedding shower.

DARK CHOCOLATE CARAMEL TART

based on recipe found in saveur magazine, issue 119.

CRUST

1 1⁄2 cups gluten-free flour (tapioca, potato starch, sweet white rice flour, arrowroot starch, sorghum flour, garfava flour)

1 tsp. xanthan gum
1⁄4 cup plus 1 tbsp. dutch-process unsweetened cocoa powder
1⁄4 tsp. kosher salt
10 tbsp. unsalted butter, cubed and softened
1⁄2 cup plus 2 tbsp. confectioners' sugar
2 egg yolks, preferably at room temperature
1⁄2 tsp. vanilla extract

CARAMEL

1 1⁄2 cups sugar
3 tbsp. light corn syrup
1⁄4 tsp. kosher salt
6 tbsp. unsalted butter
6 tbsp. heavy cream
1 tbsp. crème fraîche

GANACHE

1⁄2 cup heavy cream
4 oz. bittersweet chocolate, finely chopped
Gray sea salt for garnish

1. Make the crust: Heat oven to 350˚. Combine flour, cocoa powder, and salt in a medium bowl and set aside. Using a handheld mixer, cream the butter and sugar in a large bowl until mixture is pale and fluffy; mix in yolks and vanilla. Mix in dry ingredients. Transfer dough to a 9" fluted tart pan with a removable bottom and press dough evenly into bottom and sides of pan. Refrigerate for 30 minutes. Prick the tart shell all over with a fork and bake until cooked through, about 20 minutes. Transfer to a rack and let cool.

2. Make the caramel: In a 1-qt. saucepan, whisk together sugar, corn syrup, salt, and 6 tbsp. water and bring to a boil. Cook, without stirring, until a candy thermometer inserted into the syrup reads 340°. Remove pan from heat and whisk in butter, cream, and crème fraîche (the mixture will bubble up) until smooth. Pour caramel into cooled tart shell and let cool slightly; refrigerate until firm, 4–5 hours.

3. Make the ganache: Bring cream to a boil in a 1-qt. saucepan over medium heat. Put chocolate into a medium bowl and pour in hot cream; let sit for 1 minute, then stir slowly with a rubber spatula until smooth. Pour ganache evenly over tart and refrigerate until set, 4–5 hours. Sprinkle tart with sea salt, slice, and serve chilled.