Whip the heavy whipping cream cold from the fridge until soft peaks form and the mixture thickly coats the back of a spoon.
Cut open the vanilla beans, scraping out the seeds and adding them to the bowl with the whipping cream.
Turn the mixer on high speed and continue to whip, adding the powdered sweetener until it's fully incorporated and the mixture almost reaches the hard-peak stage.
Be careful NOT to over-whip, as this will cause the fat and the water in the cream to separate. If this happens, the ice cream will NOT freeze properly and won't have the creamy, smooth texture you desire.
Line a large loaf pan with parchment paper (or use a resealable plastic freezer-safe container, if you prefer) and scrape the cream mixture into the pan or container.
Cover with plastic wrap (or a lid) and freeze for about 6-8 hours, or until the ice cream has become solid enough to scoop.
Notes
This ice cream keeps for up to 2 weeks in the freezer, although it will get very hard if left in the freezer for more than the recommended freeze time. To make scooping easier if the ice cream is left in the freezer for a long time, simply leave the ice cream at room temperature for 10-20 or so minutes before scooping, and scoop with a spoon dipped in hot water.This ice cream freezes best in a normal refrigerator-freezer, and will become too hard if stored in a deep-freeze freezer.Feel free to use liquid stevia drops in place of the powdered stevia. Simply add them to taste. I don't recommend using granulated (baking) stevia, as the granules don't dissolve well enough in the whipping cream.