1½ tablespoons unsalted butter
1 small sprig fresh thyme
3⅓ cup fresh blueberries, divided
3 tablespoons plus 1 teaspoon granulated sugar, divided
¾ teaspoon pectin
¾ teaspoon sherry vinegar
1 tablespoon water
½ teaspoon granulated gelatin
1 large egg
¼ cup plus 1 tablespoon granulated sugar
Peel and juice of 1 lemon
5 tablespoons unsalted butter, cut into ½-inch cubes
½ cup heavy cream
One 14-ounce sheet puff pastry (thawed if frozen)
½ cup confectioners' sugar
⅓ cup crème fraîche
¼ teaspoon vanilla extract
1 tablespoon granulated sugar
1. Make the blueberry compote: In a medium saucepan set over medium heat, add the butter. Once the butter melts, add the thyme and cook, stirring frequently, for 1 minute. Remove and discard the thyme sprig and stir in 2⅓ cups of the blueberries. Add 3 tablespoons of the sugar and cook, stirring occasionally, until the blueberries have begun to break down and become very juicy, 3 to 4 minutes. In a small bowl, mix together the remaining 1 teaspoon of the sugar with the pectin. Add the sugar-pectin mixture to the blueberries and bring to a boil. Cook, stirring occasionally, until the compote is thickened and slowly falls off a wooden spoon, 3 to 5 minutes. Turn off the heat, then stir in the vinegar and the remaining 1 cup of blueberries and set aside to cool. Transfer the cooled compote to a covered container and refrigerate until the compote is chilled completely, at least 2 hours or overnight.
2. Make the lemon curd: In a small bowl, add the 1 tablespoon of water. Sprinkle the gelatin on top and set aside to bloom. In a medium saucepan set over medium heat, add just enough water to come 2 inches up the sides of the pan and bring the water to a simmer. Set a medium heatproof bowl over the simmering water (make sure the water doesn't touch the bottom of the bowl). To the bowl, add the egg, sugar, lemon peel and lemon juice and cook, stirring very frequently, until the mixture is thick and a line drawn across the back of a wooden spoon leaves a trail that doesn't immediately fill in, about 10 minutes. Add the gelatin mixture to the curd and stir until the gelatin dissolves. Transfer the curd to a fine-mesh sieve set over a medium bowl and stir to strain the curd (discard the lemon peel). To the strained curd, add the butter cubes and stir until the butter has melted. Set the curd aside to cool slightly, then cover the curd flush with plastic wrap. Refrigerate until the curd is chilled, at least 4 hours or overnight.
3. Make the puff pastry: Preheat to oven to 350°. Line a baking sheet with parchment paper. Unroll the puff pastry and place it on the baking sheet. Transfer the baking sheet to the freezer and freeze for 30 minutes. Use a fork to prick the pastry all over. Place another sheet of parchment paper on top of the puff pastry and set another baking sheet on top. Place the baking sheets in the oven and bake until the puff pastry is golden-brown, 22 to 24 minutes, rotating the tray halfway through baking. Remove the puff pastry from the oven, remove the top baking sheet and set the pastry aside to cool completely. Transfer the sheet of baked puff pastry to a cutting board and use a 3½-inch round pastry cutter to cut the cooled puff pastry into 8 rounds.
4. Make the crème fraîche: In a small bowl, stir together the crème fraîche, vanilla extract and sugar until combined and the sugar is no longer grainy.
5. Assemble the lemon tarts: Preheat the broiler. Place 4 of the puff pastry rounds on a baking sheet and dust evenly with the confectioners' sugar. Place the baking sheet under the broiler and broil until the puff pastry rounds begin to brown and caramelize, 30 seconds to 1 minute (watch the pastry closely, as broiler intensities vary). Remove the baking sheet from the oven.
6. Finish the lemon curd: In a medium bowl, add the cream and whisk until soft peaks form. Fold the whipped cream into the chilled lemon curd until just combined.
7. Use a spoon to swipe some of the crème fraîche mixture onto 4 dessert plates. Place 1 of the unbroiled puff pastry rounds on each plate. Top with a spoonful of the lemon cream followed by a spoonful of the blueberry compote. Set a caramelized puff pastry round on top. Serve immediately.