Combine 3/4 cup sugar and 3/4 cup water in a pot. Bring to a boil and cook until the sugar is dissolved, stirring occasionally. Allow to cool.
Meanwhile, melt 8 ounces chocolate in the microwave by alternating heating for about a minute and then stirring, until fully melted. (Or, melt it the old-fashioned way using a double-boiler on the stove.)
Pour the chocolate into the pot with the sugar water, and add 1 pound silken tofu, 1 teaspoon vanilla extract, 1 1/2 teaspoons ground cinnamon, and 1/2 teaspoon chili powder. Puree the ingredients using an immersion blender until smooth. (Or, blend ingredients together using a conventional blender.)
Pour into a sealed container and chill for at least 30 minutes.
Spoon into individual dishes. If desired, garnish with chopped chocolate and a dash of chili powder.