Making the Chocolate Ganache Tart is a straightforward process if you follow these steps carefully:

1. Prepare the Tart Crust:
– In a mixing bowl, combine the flour and powdered sugar.
– Add the diced butter and mix until the mixture resembles coarse crumbs.
– Stir in the egg yolk and add cold water, one tablespoon at a time, until the dough comes together.
– Form the dough into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

2. Preheat the Oven:
– Preheat your oven to 350°F (175°C) while the dough is chilling.

3. Roll Out the Dough:
– On a lightly floured surface, roll out the chilled dough to fit a 9-inch tart pan.
– Gently press the dough into the pan and trim any excess. Prick the bottom with a fork to prevent bubbling.

4. Bake the Tart Crust:
– Line the crust with parchment paper and fill with pie weights or dried beans.
– Bake in the preheated oven for about 15 minutes.
– Remove the parchment and weights, then bake for an additional 5 minutes, or until lightly golden. Allow to cool.

5. Prepare the Chocolate Ganache Filling:
– In a saucepan over medium heat, bring the heavy cream to a simmer.
– Remove from heat and add the chopped chocolate, stirring until smooth.
– Stir in the butter and vanilla extract until fully combined.

6. Fill the Tart:
– Pour the ganache filling into the cooled tart crust, smoothing the top with a spatula.
– Allow the tart to cool at room temperature for about 30 minutes, then refrigerate for at least 2 hours to set.

7. Garnish the Tart:
– Before serving, dust with cocoa powder or chocolate shavings if desired.