Fill each mold a quarter way up with sweetened prosecco.
Push one blackberry into each mold until it reaches the liquid. Cut in half if your blackberries are very large.
Fill the molds further to half way, and then add another blackberry into each mold.
Fill the molds further again, to three quarters, and add one more blackberry.
Add a little more sweetened prosecco, but do not fill the molds completely.
Cover molds and place in the freezer.
After approximately one hour, remove molds from freezer and push popsicle sticks into each mold, leaving enough stick out to handle the popsicle once ready to eat.
Return to freezer and freeze overnight.
Serve no sooner than the next day.
Notes
Remember not to fill popsicle molds completely. Prosecco will expand just a little when frozen, and therefore, if you fill the molds, the prosseco will overflow and create a mess in your freezer.