Chop the semi-sweet chocolate into fine, uniform pieces using a sharp serrated knife.
Place the chopped chocolate into a heat-proof glass bowl.
Heat the heavy cream in a small saucepan over medium heat until it begins to simmer gently.
Stir the chai spice and vanilla extract into the hot cream.
Pour the spiced cream mixture over the chopped chocolate and let it sit for two minutes.
Whisk the mixture starting from the center until it forms a smooth, glossy ganache.
Refrigerate the ganache for at least two hours until it is firm.
Scoop small portions using a melon baller and roll quickly between your palms into balls.
Roll each truffle in the cocoa powder until fully coated.