Combine the water, sugar, espresso powder, and cocoa powder in a small saucepan. Bring to a simmer, stirring occasionally to dissolve sugar. Remove from heat and set aside to cool completely.

Place the chocolate in a medium bowl. Pour the heavy cream into a glass measuring cup, and heat in the microwave until it just begins to simmer. Pour hot cream over the chocolate, cover with plastic wrap, and allow it to sit for a few minutes.

Remove the plastic wrap and stir until smooth. Allow to cool to room temperature.

In a stand mixer fitted with the whisk attachment, whip the heavy cream until stiff peaks form. Transfer whipped cream to a separate bowl, return bowl to the mixer, and replace whisk attachment with paddle attachment.

To the mixer, add the mascarpone cheese, sugar, cocoa powder, vanilla, and salt. Beat on medium speed until smooth and creamy--try not to overbeat. Add about a cup of the whipped cream and continue beating until incorporated. Gently fold in the rest of the whipped cream.

One at a time, quickly dip the ladyfingers into the mocha syrup until soaked but not soggy; arrange in an even layer along the bottom of an 8-inch square dish. (Line the ladyfingers up in two straight rows of six.***) Spread half of the the mascarpone filling on top of the ladyfingers. Drizzle half of the ganache on top. Place another layer of mocha syrup-soaked ladyfingers on top of the filling.

Spread half of the remaining filling on top of the ladyfingers. Transfer remaining filling to a pastry bag fitted with a large round tip (or a gallon ziplock bag with the corner cut off), and pipe the filling evenly over the tiramisu.