30 minutes or so, before serving, place a large mixing bowl or stand mixer bowl and whipping attachment into the freezer.
If piping, prepare your piping bag and preferred tip. I like to use a Wilton #1 star-tip.
Once cold, add the cream, vanilla, and powdered sugar to the chilled bowl. Whip on high until firm peaks can form.
Carefully transfer the whipped cream to your piping bag. Fold the bag over and do a few 'test' pipes on a clean plate.
Pipe around the edge of the tart, or design of your choice. Have fun!
Notes
I highly recommend not adding the whipped cream until right before serving. If you choose to use a stabilizer like gelatin or agar agar, you can pipe several hours in advance.