Whisk together the egg yolk, cream, and vanilla in a small bowl.
1 egg yolk, 1 Tablespoon heavy cream, 1/2 teaspoon vanilla extract
Combine the flour, powdered sugar, and salt in a food process and briefly process to combine. Add the cold butter pieces to the flour mixture and pulse to cut into the flour until the mixture resembles coarse meal, about 15 pulses.
1 1/4 cups (156g) all-purpose flour, 2/3 cup (65g) powdered sugar, 1/4 teaspoon salt, 8 Tablespoons cold salted butter
While the food process is running, add the liquid through the feed tube and continue to process just until the dough comes together around the blade.
Turn out the tart dough onto a sheet of plastic wrap and flatten into a 6-inch disk, then wrap it tightly and refrigerate for 1 hour. Let sit out on the counter for 10 minutes to soften slightly before rolling out.
Roll out the pastry crust on a lightly floured surface until it is slightly larger than your tart pan (mine is a 9-inch pan). Carefully transfer the dough to the pan by rolling it onto the rolling pin, then gently easing the dough into the pan, pressing into the corners and fluted sides of the pan.
Run the rolling pin over the top of the pan so that the excess dough gets cut off on the edge of the pin, making a clean edge. Patch any edges that are too thin with excess dough, trimming away the edge again as necessary. Freeze the tart shell for 30 minutes.
When ready to bake the tart shell, heat oven to 375 degrees F. Press a double layer of foil into the frozen tart shell, covering the edges of the pan and filling the tart shell with pie weights. Bake for 30 minutes, rotating halfway through, then carefully remove the pie weights and foil and bake another 5 to 10 minutes, until the tart shell is fully baked and golden. Cool completely before filling.