For the hazelnut ganache: Put the chocolate couverture in a medium bowl and set aside. In a medium saucepan, scald the heavy cream. Pour the scalded heavy cream over the chocolate couveture and set aside for 3 to 5 minutes to allow the scalded milk to melt the chocolate. With a rubber spatula, gently stir the chocolate and heavy cream until fully blended and smooth. Add the butter and stir with a rubber spatula to incorporate. Add the hazelnut extract and stir to incorporate. Pour the mixture into a large pastry bag and set aside.
Pre-treat the polycarbonate chocolate mold with red (or any color desired) cocoa butter. Once the cocoa butter is set, brush each mold with a thin layer of tempered chocolate. Fill the entire mold with the fluid tempered chocolate and tap on work surface to release air bubbles. Quickly invert the mold and tap out excess chocolate. With a putty knife, scrape off the rest of the chocolate, let the mold rest upside down for 1 minute, and then scrape off surface of mold again. Let the chocolate set. Fill each mold with hazelnut ganache, 3/4 of the way full. Let the hazelnut ganache set. Pour the fluid tempered chocolate over the mold and spread thin, scraping off any excess. Tap mold on surface to release any air bubbles, and then scrape excess chocolate again. Transfer the finished mold to the freezer and let set for 2 to 3 minutes. Pull out the mold, invert, and tap on clean work surface to release finished bonbon.
To assemble: Dip the hazelnuts in fluid tempered chocolate and let set. Attach to finished bonbons with a small dab of tempered chocolate. With a small pastry bag, pipe the tempered chocolate on parchment paper in a 1 1/2-inch upside-down V-shape. Repeat to make 80. Once set, lift the piped tempered chocolate and attach to the bonbons with a small dab of tempered chocolate to look like the legs of a spider.
Tempered Dark Chocolate Couverture:
Over a double boiler, melt 1 pound 4 ounces chocolate to 115 to 120 degrees F. Bring the bowl with the melted chocolate to a flat, clean work surface (preferably marble or stainless steel ), wiping away any access water or steam from the bowl. With a rubber spatula, fully incorporate the remaining 2 ounces chocolate. Bring down the temperature of the chocolate to 80 to 84 degrees F by either stirring constantly in a figure 8 motion, or tabling (see Cook's Note). Once cooled, test the chocolate by dipping a small strip of parchment paper into the melted chocolate, and then lay it down on a clean work surface. If tempered, the chocolate on the parchment paper should be dry, hard, shiny, and without any streaks in 3 to 5 minutes. If any of these occur, keep stirring (agitating) the chocolate, or table it again, until a parchment paper test shows that the chocolate is tempered. When tempered, bring the chocolate back to the double boiler and reheat to NO HIGHER than 89 degrees F. (Bringing the temperature back up aids in a more fluid working consistency.) Transfer the chocolate to a chocolate warmer or set the bowl on top of a heating pad (at medium setting) to keep in temper.
To table, pour 2/3 of the chocolate onto a marble slab, quickly spread with a thin metal spatula, scrape into a pile with a putty knife, and then spread thin again. Repeat until the right consistency is reached. Add back to the warm chocolate.