01 - Preheat your oven to 350°F (175°C). Lightly grease a 9-inch tart pan with a removable bottom.
02 - In a food processor, combine almond flour, all-purpose flour, powdered sugar, and salt. Pulse to blend. Add the cold, cubed butter and pulse until the mixture resembles coarse crumbs.
03 - Add the egg yolk and 1 tablespoon of cold water to the food processor. Pulse until the dough just begins to come together, adding an additional tablespoon of water if needed to achieve this consistency.
04 - Evenly press the dough into the prepared tart pan, extending it up the sides. Prick the base thoroughly with a fork. Place the tart pan in the refrigerator to chill for 15 minutes.
05 - Bake the chilled crust in the preheated oven for 18–20 minutes, or until it achieves a light golden hue. Remove from the oven and allow to cool completely.
06 - While the crust cools, gently heat the heavy cream in a saucepan until it just begins to simmer. Pour the hot cream over the chopped dark chocolate in a mixing bowl. Allow to stand for 2 minutes, then stir in the butter until the mixture is completely smooth and glossy.
07 - Pour the prepared chocolate ganache into the completely cooled tart crust. Spread the ganache evenly to create a smooth surface. Place the tart in the refrigerator to set for approximately 1 hour.
08 - In a small saucepan, combine the pitted and halved dark cherries, granulated sugar, lemon juice, and 1 tablespoon of water. Cook over medium heat for 5–7 minutes, stirring occasionally, until the cherries begin to release their juices.
09 - Whisk the cornstarch into the cherry mixture and continue to cook for another 1–2 minutes, stirring, until the topping has thickened. Remove from heat and allow to cool to room temperature.
10 - Once the ganache is set and the cherry topping has cooled, spoon the cherry mixture evenly over the chocolate ganache. Return the tart to the refrigerator and chill until ready to serve.