Place the flour, sugar, and salt in the bowl of a food processor, stand mixer, or in a medium mixing bowl.

Pulse/stir/cut in the butter with a pastry blender, until the mixture resembles coarse meal.

Add the egg yolk, cream, and vanilla, and process/mix/stir until the dough gathers itself into a ball and pulls away cleanly from the sides of the bowl.

Wrap the dough tightly in plastic wrap, and chill for 1 hour.

On a lightly floured surface, roll the dough until it's an inch or two wider than your tart pan.

Press the dough gently into the pan(s), trimming away any excess.

Line the tart pan with parchment paper and pie weights.

Bake the tart shell at 375°F for 18 to 22 minutes, or until completely set and beginning to turn golden brown around the edges. Let the crust cool for 15 minutes before making the ganache.

Add the whipping cream and butter to a small sauce pan and warm over low heat until the butter is melted. Then bring the cream/butter mixture to a gentle simmer.

Pour the warm cream/butter mixture over the chopped chocolate and let it sit for 3 minutes to soften the chocolate.

Stir with a metal spoon or silicone spatula until combined and smooth.

Then pour the ganache into the cooled tart shell and allow to set up. This should take about an hour in the refrigerator or a few hours on the counter.