Place the ground almonds, confectioners sugar and orange blossom water into a medium saucepan and cook over low heat for about 7 to 8 minutes until a uniform paste comes together that, when touched, no longer sticks to your fingers.
Break this almond mixture into pieces and add to the bowl of a strong food processor.
Add the melon and orange confit pieces. Pulse a couple of times, then process until everything is fully mixed. You don’t want any big lumps of the fruit confit.
Place the wheat starch paper on a rimmed 10-inch x 15-inch baking pan, and set aside.
On a marble or stone countertop, using your hands, form the fruit paste into as flat a rectangle as possible.
Scrape the rectangle onto a piece of cling film, cover with another piece of cling film and roll to a rectangle approximately 10-inches x 15-inches.
Remove the top piece of cling film, and carefully flip the paste into the baking sheet on top of the wheat starch paper.
Remove the other piece of cling film and continue to press into the baking pan to fit the piece of wheat starch paper. If it’s sticking too much, use a wet spatula to smooth out the top.
Let the fruit paste sit, uncovered, in a warm, dry place for up to seven days until it reaches a firm and dry (only slightly tacky) consistency. Using a Calisson-shaped cutter, cut as many pieces as possible, and as close together as possible, to avoid wasting any of the fruit paste. It helps to dip the cutter in water from time to time. Also, you need to press hard on the cutter to get through the wheat starch paper. Alternatively, using a wet, sharp knife, cut the Calissons into elongated diamond shapes.
Set cut Calissons on a tray and let dry while you prepare the royal icing.