Position a rack in the center of the oven and heat the oven to 400°F. Generously butter a 10-inch springform pan and wrap the bottom and sides in heavy-duty aluminum foil. Have ready a roasting pan just big enough to accommodate the springform, and put a kettle of water on to boil.
Make the ganache. Dissolve the espresso powder in 1 Tbs. hot water and add it to the warm ganache still in the food processor. Process until fully incorporated, about 10 seconds. Transfer the espresso-flavored ganache to a large bowl.
In the bowl of a stand mixer fitted with the whisk attachment, whip the eggs, sugar, and flour at just under high speed until pale, light, and fluffy and at least doubled in volume (if not tripled), about 6 minutes. Add about one-third of the egg mixture to the ganache and mix with a rubber spatula until combined. Add the remaining egg mixture and gently fold together until just combined and no obvious streaks of egg remain.
Pour the batter into the prepared springform pan. Set the pan inside the roasting pan and fill the roasting pan with 1 to 1-1/2 inches of boiling water. Bake until a dry crust forms on the top of the torte and the edges seem set but the center is still a bit wobbly when you jiggle it, 15 to 20 minutes. Remove the torte from the water bath and its foil wrap. Cool the torte on a wire rack to room temperature and then refrigerate until cold and completely set, at least 3 hours or overnight.
To unmold, carefully remove the springform ring. Put a piece of plastic wrap over the top of the torte. Invert the torte onto a baking sheet and remove the pan bottom; use a thin-bladed knife to help separate the torte and pan bottom if necessary. Invert the torte again onto a serving plate and remove the plastic wrap. Just before serving, put the confectioners’ sugar and cinnamon in a small fine strainer and sift over the top of the torte.
To cut the torte as cleanly as possible, dip your knife in hot water to heat the blade and wipe dry before each cut. Or for a cleaner cut, use unwaxed dental floss.