Method
Preparation
Preheat your oven to 350°F (175°C).
Whisk together the flour, cocoa powder, and powdered sugar in a large bowl.
Add the cold, cubed butter to the dry ingredients and mix until it resembles coarse crumbs.
Stir in the egg yolk and enough cold water until the dough comes together.
Wrap the dough in plastic wrap and refrigerate for about 30 minutes.
Roll out the chilled dough to about 1/8-inch thickness.
Cut out circles and press them into mini tartlet pans.
Prick the bottoms of the tart shells with a fork and bake for 10-12 minutes.
Let cool completely before filling.
Ganache Preparation
Heat the heavy cream in a small saucepan over medium heat until it begins to steam.
Remove from heat and add the chopped chocolate; let sit for a minute, then stir until smooth.
Stir in the vanilla extract and pinch of salt.
Pour the ganache into each cooled tart shell.
Refrigerate for at least 1 hour to allow the ganache to set.
Garnish with whipped cream, chocolate shavings, or fresh berries before serving.
Serve chilled or at room temperature.
Notes
For an elegant finish, sprinkle with a dusting of cocoa.