For the dacquoise: Put two oven racks equidistant from the top and bottom of the oven and preheat to 225°F. Trace three 8" circles on two pieces of parchment. Turn the parchment over on two baking sheets so the ink side is facing down., Place the egg whites, cream of tartar, and salt in the bowl of a stand mixer and beat on medium speed until fine bubbles form. Increase the speed to medium-high and whip until soft peaks form. With the mixer running, gradually add the sugar and whip until the meringue is stiff and shiny but not dry., In a small bowl, whisk together the nut flour and cocoa powder. Sprinkle half of the mixture over the egg whipped egg whites and use a spatula to fold into the whites. Repeat with the second half of the cocoa mixture, folding just until the color is uniform and no longer streaky. The mixture should be smooth and thick., Using a piping bag or small spatula, form disks of batter inside the circles on the parchment., Bake the disks for 1 hour. Turn off the oven, and leave the disks inside to dry for at least 3 hours, or as long as overnight., For the caramel whipped cream: Place the caramel in a medium heatproof bowl with 1/2 cup of the heavy cream. Heat in the microwave in 20-second bursts, stirring in between, until the mixture is smooth. Stir in the remaining heavy cream. Place in the bowl of a stand mixer and put the bowl in the refrigerator for at least 1 hour., When ready to assemble the cake, beat the mixture until soft peaks form. Add the salt and confectioners' sugar and beat until the cream holds a medium peak., For the hazelnut filling: In the bowl of your mixer, combine all of the ingredients and beat with the whisk attachment until fluffy and smooth., To assemble: Place one of the dacquoise disks on a serving plate and pipe marble-sized spheres of the hazelnut filling onto it, leaving some spaces in between for the whipped cream. Spread a third of the caramel whipped cream over the hazelnut filling and top with the second disk. Pipe with the remaining hazelnut filling and another third of the whipped cream. Top with the last disk, piling the remaining whipped cream on top. Sprinkle with chopped nuts., Refrigerate any leftover dacquoise for up to 2 days; the meringue layers will continue to soften as the cake sits.