Preheat the oven to 350°F (170°C).
Grease a 12 cup (large) bundt pan well with butter, or spray with quick release cake spray.
Cream the butter and sugar together thoroughly with a hand-held electric mixer or using a stand mixer.
Add the eggs and vanilla and mix together well.
Sift the flour, cocoa, baking powder, salt and cinnamon together into a medium bowl. Set aside.
Beat together the cooled coffee and the buttermilk.
Add the flour mixture to the batter alternately with the coffee/buttermilk mixture, beating after each addition. (Use two additions of the flour mixture and two of the liquid mixture.)
Pour the mixture into the bundt pan.
Bake for 35 to 45 minutes or until the top springs back when touched lightly and a skewer inserted in the cake comes out clean.
Cool in the pan for ten minutes before removing to a wire rack to cool completely.
When the cake is at room temperature, prepare the glaze.
For the glaze, sift together the confectioner's sugar and cocoa, if using, into a medium bowl.
Gradually add the coffee, a tablespoon at a time, until a thick glaze consistency is reached.
Beat in the corn syrup or golden syrup, whisking furiously to create a smooth, glossy glaze.
Drizzle carefully over the cake, and garnish as desired.