Start with cranberries and strawberries that are frozen. Add them to a pot and fill the pot with water (not what is listed in the ingredients) until the berries are just covered. Cook the berries over medium heat until they simmer and burst in the pot. Keep cooking them until they’re soft enough to mash with a fork.
Step 2
Remove the pot from the heat, and use an immersion blender to blend the ingredients into a red syrup. Strain the syrup into a cocktail shaker and discard the pulp and seeds. Add lemon juice, liquid stevia, more water, and your vodka to the shaker.
Step 3
Seal and shake your shaker vigorously until you feel the cocktail turn cold. Fill clean glasses with new ice, and strain, and divide the cocktail amongst the glasses. Fill the remainder of each glass with carbonated water that’s either plain or flavored with lemon or lime (not listed in ingredients).