Roast the nuts: Preheat the oven to 350 degrees F. Place a cup of the chopped almonds with 1/4 cup corn syrup in a 2-quart heavy-bottomed saucepan and place over low heat to liquify the corn syrup. You only want to heat the mixture until the corn syrup is thin enough to coat the nuts evenly; this will take 3 to 4 minutes. Remove the saucepan from the heat. Using a large slotted spoon, allow the excess corn syrup to drain as you scoop the coated nuts onto a parchment paper-covered baking sheet. Repeat method with the pistachio and the hazelnuts. Be sure to spread them in an even layer so they will roast evenly in the oven.
Bake until they are evenly caramelized, 15 to 20 minutes. To test for doneness, you can also break a nut in half and check to see if it is light brown on the inside. Keep an eye on the nuts because the sugar will burn very soon after it caramelizes. Remove the baking sheet from the oven and place on a wire rack. When the nuts are completely cooled, break apart any that are clustered together.
Fill a cornet half full with the tempered bittersweet chocolate. Pipe a chocolate circle 3 1/2 inches in diameter onto a parchment paper-covered baking sheet. If you do not have a cornet, you can use a spoon; drop a spoonful of the chocolate onto the parchment paper and spread it into a 3 1/2-inch diameter circle with the back of the spoon. In either case, keep the thickness of the circle as even as possible. Make about 5 circles. Then, create your own design as you top each circle with the nuts and fruits. Work quickly, or the chocolate will set before you've accomplished this. If the nuts and fruit do not stick to the chocolate, lightly dip them in the bowl of tempered chocolate and "glue" them to the top of the disk. When you finish these, repeat the process until you have used all of the tempered chocolate, nuts, and fruit.