In a medium sauce pan, bring the water to a rolling boil over medium-high heat. Add the butter one piece at a time, whisking to combine after each addition. Remove from the heat and add the chocolate. Stir until completely smooth; set aside.

In another medium bowl, whisk together the flour, sugar, salt and espresso powder. In a separate bowl, whisk together the milk, eggs, and vanilla. Gradually add the milk mixture to the flour mixture, whisking until smooth. Gradually add the chocolate mixture, whisking until smooth. Transfer to an airtight container and refrigerate overnight. Once rested, pour and press through a fine-mesh sieve; discard any lumps.

Lightly coat an 8-inch crepe pan or 10-inch non-stick skillet with melted butter and heat over medium heat; wipe out excess. Pour about 3 tablespoons of batter into the pan, swirling to coat bottom. Reduce the heat to medium-low and cook the crêpe, flipping once until edges are golden and center is set, about 30-45 seconds per side. Transfer crepe (I invert the pan with a whack on the counter) to a sheet of waxed paper. Continue with remaining batter (no butter needed for non-stick skillet), placing a sheet of waxed paper between each crepe. Crêpes can be made and refrigerated for up to one day.

In a medium bowl using a wire whisk or a hand held mixer, beat the cream until soft peaks form, about 3-5 minutes. Refrigerate until ready to use.

Whisk egg whites and sugar in the bowl of a stand mixer set over a pan of simmering water. Stir until the sugar has dissolved and the mixture registers 160º F on a candy thermometer, about 3 minutes. Remove from the heat and place the bowl on the stand mixer fitted with the whisk attachment. Beat on high until slightly cooled and stiff (not dry) peaks form, about 5 minutes. Switch the whisk attachment for the paddle attachment. With the mixer on medium-low speed, add the butter, a few pieces at a time, mixing well after each addition (meringue will deflate slightly as butter is added). Add vanilla, Frangelico, Nutella, and salt; beat until the mixture comes together, about 5-7 minutes.  (Mixture will separate at first. If the mixture looks grainy, place in the refrigerator to cool. Then beat again until smooth and fluffy). Using a rubber spatula, fold in the refrigerated whipped cream; use immediately.

Place an 8-inch round of parchment paper over a wire rack set over a rimmed baking sheet. Place a crêpe on top of the parchment. Evenly spread about 3 tablespoons of filling on top of the crêpe. Top with another crêpe. Continue layering with filling and crepes, using about 32 crêpes and ending with a crêpe on top. Refrigerate until firm, at least one hour.

In a medium saucepan over medium-high heat, bring the cream, corn syrup, and salt to a boil. Remove from the heat and add the chocolate. Let stand for 5 minutes, then stir until completely smooth. Cool completely before using.

Combine the sugar and water in a medium saucepan over medium heat. Cook until the sugar dissolves. Bring the mixture to a boil. Without stirring, continue to cook until the mixture turns a light amber color. Remove from the heat and add the hazelnuts, stirring to coat. Pour the candied hazelnuts onto a piece of parchment paper and spread to an even layer. Allow the mixture to cool completely. Break or chop into smaller pieces.