Step 1Heat the oven to 325 degrees.
Step 2Spray a 9-by-13-inch baking dish with nonstick cooking spray and line the bottom of the dish with a piece of parchment paper.
Step 3Whip the cream in a large mixing bowl with a wire whisk or an electric mixer on high speed until soft peaks form. Cover the bowl with plastic wrap and place it in the refrigerator until you are ready to use it.
Step 4Set a metal bowl over a pot of water or fill the bottom of a double boiler with water and bring the water to a simmer (not a boil) over medium-high heat. Remove the bowl from atop the pot and combine the chocolate, espresso and 2 tablespoons of water in the bowl. Set the bowl back over the simmering water and warm the chocolate, without stirring, until it melts, 15 to 20 minutes. Remove the bowl from atop the water and set it aside but keep the water simmering.
Step 5Combine the eggs, egg yolks and sugar in a mixing bowl (the kind used with a stand mixer). Place the bowl over the simmering water and whisk by hand until the sugar is dissolved and the mixture is slightly warm, about 5 minutes. Fit the bowl onto the stand mixer and whisk it on high speed until the mixture is light yellow, foamy and triple in volume, 5 to 7 minutes.
Step 6Turn the melted chocolate out into a large mixing bowl. Add one-third of the whipped eggs and sugar to the bowl with the chocolate and use a rubber spatula to gently fold the eggs into the chocolate, scraping down the sides of the bowl as you mix. Fold only until the batter is streaky and not fully combined. Add another third of the egg mixture and fold it in, again just until the batter is streaky. Add the remaining egg mixture and fold it in just until the batter is streaky. Remove the whipped cream from the refrigerator and gently fold it in, scraping down the sides of the bowl, until the ingredients are fully combined and the batter is uniform in color.
Step 7Spoon the batter into the prepared baking pan. Ssmooth the batter out to an even surface (using a metal offset spatula if you have one). Place the baking dish in a larger baking dish or roasting pan and fill the larger dish or pan with one-half-inch of hot tap water. Cover the larger baking dish tightly with aluminum foil, so that both dishes are covered. Pierce the foil in several places with a sharp knife and put the cake in the oven to bake for 20 minutes. Remove the cake from the oven and carefully lift off a corner of the foil to release the steam. Replace the foil and return the cake to the oven to bake for 30 more minutes, until the center of the cake is set and feels foamy, not liquidy, when you touch it gently with your finger. Remove the cake from the oven, lift the baking pan out of the water bath and place it on a wire rack to cool to room temperature. Cover the baking pan tightly with plastic wrap and place it in the refrigerator to chill for at least 2 hours or up to overnight.
Step 8Two hours before you are ready to serve the cake, line a cutting board with parchment paper. Remove the cake from the refrigerator, remove and discard the plastic wrap and turn the cake out onto the prepared cutting board. Measure the serving area of the dinner plate you want to serve this dessert on to make sure the pieces of cake will fit. (Ours is 7 inches.) Trim the sides of the cake, using a ruler, so that each piece of cake will be as long as the inner diameter (inside the rim) of your plate. Measure the long side of the cake and make a score every 2 inches. Turn it around and do the same thing on the other side, making your first score 2 inches from the edge. Wipe the knife off with hot water between each cut. Use a long sharp knife to cut from the lower left corner of the cake to the first score on the upper side to create very thin triangles.
Step 9Set the cake slices aside to come to room temperature before serving.
Step 10To serve, if the hot fudge sauce has cooled, warm it in a saucepan over medium-low heat, stirring constantly to prevent it from burning, until it is warm but not boiling. Run your knife under one of the cake slices to pick it up and lay it across the center of a dinner plate. Repeat with the remaining slices. Spoon 2 tablespoons of the fudge sauce in the center of each cake slice so that it spills off to either side of the slice, creating a wide band across it. Garnish the plate with the candies and serve.