Make the devil's food cake: Position a rack in the center of the oven and preheat to 350 degrees F.
Butter the bottom and sides o f a 17 1/2 by 11 1/2-inch jelly roll pan and line the bottom with baking parchment or waxed paper. Lightly dust the sides of the pan with flour and tap out the excess.
In the 4 1/2-quart bowl of a heavy-duty electric mixer, place the cake flour, sugar, cocoa powder, and baking powder. Using the paddle attachment, blend the dry ingredients on low speed, until combined.
Add the butter, one tablespoon at a time and continue to mix until the mixture resembles coarse meal.
At medium speed, beat in the water, scraping down the side of the bowl as necessary. Continue to beat the batter at medium speed for 2 minutes.
Beat in the eggs, one at a time, scralling down the sides of the bowl with a rubber spatula after each addition.
Scrape the batter into the prepared pan and, using an offset metal cake spatula, smooth it into an even layer.
Bake the cake for 18 to 22 minutes, until the cake springs back when gently touched in the center.
Run the tip of a knife around the edges of the pan. Invert the cake on to a wire rack. Carefully peel off the paper and cool the cake completely.
Make the chocolate espresso whipped garlache:
In a small cup, stir the espresso powder into the hot water until dissolved; set aside
Place the chocolate in a medium bowl: set aside.
In a small, heavy saucepan, combine the heavy cream and espresso mixture. Bring to a gentle boil.
Remove from heat and pour the mixture over the chocolate. Allow the mixt ure to stand for 1 minute to melt the chocolate. Gently whisk until smooth.
Cover the bowl and refrigerate the ganache for 2 hours, until chilled and slightly thickened.
Using a hand-held electric mixer, beat the ganache just until lightened in color, about 30 seconds. Do not overbeat the ganache or it will become grainy.
Assemble the cakes: Using eight 3-inch (2 inches in height) metal ring molds, cut out 8 rounds of the devil's food cake. Place the molds on a baking sheet and place a cake round in the bottom of each mold.
Fill a pastry bag fitted with a large plain tip with the whipped ganache. Pipe the ganache on top of each round, filling each mold to the top.
With a small, offset metal spatula, scrape the top of each mold to the level the ganache. Place the sheet of molds in the freezer for 2 hours.
Make the glaze: Place the chocolate in a medium bowl.
In a small saucepan, bring the cream and corn syrup to a gentle boil.
Pour the hot cream over the chocolate and let the mixture stand for 1 minute to melt the chocolate. Gently whisk until smooth.
Cover the surface of the glaze with plastic wrap and let it stand at room temperature until ready to glaze the cakes.
Make the chocolate espresso fudge sauce: In a medium saucepan, stir together the cocoa, espresso powder and sugar.
Slowly whisk in the milk and cream.
Stir in the corn syrup. Cook over medium heat, stirring constantly until the sugar is completely dissolved.
Raise the heat to medium-high and while continuing to stir, bring the mixture to a boil.
Remove the pan from the heat and add the chocolate. Let the mixture stand for 30 seconds to melt the chocolate. Whisk until smooth.
Stir in the butter and vanilla.
Unmold and glaze the cakes: Remove the molds from the freezer.
Gently heat the side of each mold using a portable hair dryer or a hot, damp towel. Carefully slide off each mold.
Place the cakes on a wire rack set over a baking sheet. Place the baking sheet in the freezer for 15 minutes.
Remove the plastic wrap from the glaze and gently whisk until smooth.
Remove the desserts from the freezer and pour the glaze over each cake to coat it completely.
Place a spoonful of chocolate espresso fudge sauce on a dessert plate. Place a cake on top of the sauce; garnish with a candied violet, if desired.