Vanilla-Scented Shortbread

Position oven rack in the lower third of the oven; preheat oven to 300.
Have two 7 1/2 inch fluted tart pans with removable bottoms or two 9-inch glass pie pans at hand.
Using a paring knife, split the vanilla bean lengthwise; scrape the tiny seeds of the vanilla bean into a small bowl; discard the bean and set the seeds aside.
Add the flour, cornstarch, and salt to the bowl of a food processor and pulse until blended.
Add the sugar, vanilla bean seeds, and orange zest; profess a few seconds, until blended.
Scatter the butter cubes over the flour mixture and pulse 6 or 7 times, then process for 6 seconds, or until the crumbs are fine and powdery.
Process another 5-7 seconds, until the crumbs are clumpier and the dough holds together easily when pressed.
Press the dough evenly and firmly into the tart pans (if using pie pans, press the dough only into the bottom of the pans, not the sides.
Press the back of the tines of a fork all around the edges of each pan, and sprinkle the shortbread with the coarse sugar.
Bake for 40-45 minutes, until it is just barely colored a creamy beige; don't let it brown.
Place the pans on a wire rack and let cool for 15 minutes.
Remove the rims of the pans if you are using tart pans, and cut each round into 12 wedges while it is still very warm.
Transfer the triangles to the wire rack and cool completely.
Store in an airtight container at room temperature for up to a week.