Preheat the oven to 325 degrees F. Butter an 8-by-2-inch round cake pan, line the bottom with parchment paper, then butter and flour the pan, tapping out the excess flour.
Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment until light and fluffy. With the mixer on low, add the eggs, one at a time, then mix in the chocolate syrup and vanilla. Add the flour and mix until just combined. Pour the batter into the prepared pan and bake for 40 to 45 minutes, until just set in the middle. Allow to cool in the pan for 30 minutes, then remove from the pan, turn the cake upside down on a wire rack set over a sheet pan and cool completely.
For the icing, whisk together the confectioners' sugar with 1 tablespoon water until smooth, thick and just barely pourable. When you lift the icing from the bowl with the whisk, it should slowly fall back on itself in a ribbon. (You may need to add a few more drops of water.) Fit a pastry bag with a small round pastry tip and fill it with the icing. Set aside while you make the ganache.
For the ganache, place the heavy cream, chocolate chips and coffee in a bowl set over a pan of simmering water and heat the mixture until smooth and warm, stirring occasionally. Pour the ganache evenly over the top and sides of the cake, tilting the rack until the ganache is smooth all over.
Immediately, before the ganache sets, pipe parallel lines about 1 inch apart on the entire cake, stopping just short of the edge. Lightly drag the back of a small paring knife through the ganache perpendicular to the white lines also 1 inch apart, alternating directions (first left to right, then right to left, and so on) and covering the whole cake. Allow the ganache and icing to set. Cut into wedges and serve at room temperature.
You can wrap and refrigerate the cake for a few days, but once it is ganached, leave it at room temperature for up to 8 hours. If you refrigerate it, beads of condensation will form on the ganache and damage the decoration.