Marlow & Sons' Most Amazing Chocolate Caramel Tart

My mom once told me, "If at first you don't succeed, try (and try) again." 
That's pretty much how I feel about this absolutely amazing Chocolate Caramel Tart...
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We invited Kathyrn and Ed over for dinner, for the first BBQ on our balcony. Oh you heard me right, I said balcony! Outdoor spaces are at a premium in Brooklyn and while our new abode lacks many things (square footage, for example), outdoor space--I'm happy to report, it's got! I made Heidi Swanson's Summer Squash Soup with Tofu Croutons and Thai Red Curry (Doubles? yes, please!) and Kat made a potato salad that hit the spot. There was barbeque fare and I made a vegetarian burger topped with a spicy mayo dip and some avocado for our vegetarian guest (which was really just me).
...then it was time for dessert.  
Ever since I started re-reading back issues of Saveur magazine, I've been wanting to make the Chocolate Caramel Tart from Marlow & Sons (Marlow & Sons is kind of like the big jewel in a crown that includes Diner and Roman. I think it has some of the most delicious food in Brooklyn right now.) Then I saw photos of the very same tart on Lottie + Doof, one of my favorite food bloggers. I was salivating. I had to make this tart and this BBQ was the perfect occasion.
I also wanted to do something special for Kat and Ed because they have been so, so tremendously helpful to us. They have baby-sat Otis more times than I can count on my fingers and toes, and they offer to watch him. Kat would say, "Hey Bats, we'd love to spend some time with Otis next week. Let us know if you want us to come over." Can you believe it?! We aren't even related by blood. They go above and beyond...
So I thought this tart was the perfect 'Thank You.' You can imagine, then, how bummed I was when it turned out that the caramel part of the tart was all wrong. I'd never made caramel before and I made an amateur mistake. I knew it immediately and it was confirmed when I sliced the tart for serving. Whaa. Boo Hoo. Sob. Sob.
I felt defeated. I was bummed. I didn't have a candy thermometer and I (incorrectly) guessed that step #2 (see below) would only take a minute or two after the sugar came to a boil. Turns out it takes around 15 minutes for sugar to caramelize and the best way to determine whether your caramel is done is by color. You can do this by cooking the sugar (before you add the butter, cream and creme fraîche) in a pot with a light color bottom like white enamel. Color, color, color. The color should be a deep, rich amber-- the color of caramel. The boiling sugar (remember, without stirring or interference) starts to turn a light brown color and then gets deeper and deeper. Then, off heat, you add the remaining ingredients. My first caramel filling was a murky white and pretty much looked like sugar sludge. No good. I just didn't give it enough time. I'm not sure what I was thinking! Again, it should take between 12 and 15 minutes for the sugar to caramelize-- but remember, color is key! Lesson learned. 
So while we all thought the original crust was perfect and the ganache was to-die-for, the caramel filling needed some work.  
And, if at first you don't succeed, try again. This is me...trying again! I'm glad I did. The tart came out perfectly. I'm going to drop some off for Kat and Ed. Personal delivery of two amazing slices of chocolate caramel tart?  I think that delivers the 'Thank You' message loud and clear!

Chocolate Caramel Tart (Courtesy of Saveur Magazine and inspired by Lottie +  Doof)
Serves 8
For the Crust:

1 1⁄2 cups flour
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
For the 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
For the 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° (the recipe in the hard copy of Saveur said 365-- but I'm going by the color). 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.