Add the whiskey and simple syrup into a mixing tin.
Add a little boiling water to an Irish Coffee mug to heat it, and nestle the tin in the mug so that the tin heats as well.
Add the heavy cream to a separate mixing tin, and dry-shake (without ice) until the cream thickens.
Dump the water out of the mug, add the whiskey-sugar mixture, and fill with boiling water to about 1 inch below the rim.
Pour the espresso shot followed by the thickened cream on top, and grate cinnamon.