Soften the vanilla ice cream at room temperature (or in the microwave).
Pour 1 tablespoon (15ml) into each popsicle mold.
Freeze for 2-3 hours, until firm.
Prepare root beer layer:
In the meantime, open the can or bottle of root beer soda and let it sit in the refrigerator.
After a few hours, pour root beer into a large measuring cup.
Whisk in a little (about 2 Tbsp) vanilla ice cream into the root beer, and remove excess foam and bubbles with a spoon.
Continue to stir in the ice cream, a little bit at a time.
Once all the vanilla ice cream has been incorporated into the root beer, remove the popsicle molds from the freezer and stir and pour the root beer mixture into the molds.
Add the popsicle mold cover and insert the popsicle sticks.
Freeze for 6-8 hours, until solid.
Once fully frozen, remove the popsicles from the molds and enjoy immediately.
Notes
Either leave the popsicles to warm up at room temperature for a few minutes before removing, or run the molds under warm water to help with releasing.