In the bowl of a stand mixer, combine the flour and butter. Mix on low speed until mixture resembles coarse sand.
Add powdered sugar and vanilla bean paste (see note) and mix to combine.
Add egg yolk and milk. Mix just until combined.
Turn the dough out onto your work surface and gently work into a ball. Form the dough into a disc, wrap in plastic, and chill in the refrigerator for at least an hour.
After chilling, remove the dough from the refrigerator and roll on a lightly floured surface to a thickness of about ¼ inch. Line a 9" tart pan with removable bottom (see note) with the dough. Place the tart pan on a baking sheet and chill in the refrigerator until ready to assemble tart.
For Filling
Preheat oven to 400° F.Pit and slice plums. Place plum slices as desired in the prepared crust. Sprinkle the plums with the vanilla sugar (see note).
Bake 22-25 minutes, or until crust is golden. Allow tart to cool in the pan before removing it. Serve the tart with vanilla ice cream, if desired.
The tart can be stored at room temperature, covered loosely, up to one day. You can extend the life of the tart, covered in the refrigerator, for up to three days, but it will be best the day it's baked.Enjoy!
Notes
Note on vanilla bean paste: I love the beautiful vanilla bean flecks in this dough *almost* as much as I love the flavor! If you'd rather substitute, you can add an equal measure of vanilla extract instead.Note on tart pan: I used a 9" tart pan with removable bottom for this recipe. I prefer a pan that is lighter in color (as opposed to the darker, non-stick pans) because the crust browns more slowly. Note on vanilla sugar: I didn't use much vanilla sugar in the tart, because I didn't want it to be overly sweet (perfect to have with a scoop of ice cream). If you'd prefer a sweeter tart, you can add more. You can buy vanilla sugar online, or make some for yourself with my Homemade Vanilla Sugar recipe (it makes a fantastic gift, too)!