In a large mixing bowl, combine the cooled brewed coffee, milk, sweetened condensed milk, cocoa powder, and vanilla extract. Whisk until everything is thoroughly mixed and smooth.
If using, add chocolate chips to the mixture and stir gently to distribute.
Pour the coffee mixture into popsicle molds, filling them about 3/4 full to allow for expansion.
Insert the popsicle sticks and place the molds in the freezer.
Freeze for at least 6 hours, or until the popsicles are solid.
To release the popsicles, run lukewarm water over the outside of the molds for a few seconds, then gently pull them out.