Combine coffee, half & half, sugar and chocolate syrup in a small saucepan and simmer, over low heat, stirring until sugar dissolves. Set aside to cool and stir in the vanilla extract.
Pour into a baking pan and place in the freezer for approximately 90 minutes.
Stir every 30 minutes with a fork. Once mixture is firm, transfer it to a bowl and stir rapidly with a fork until the texture becomes slushy.
