You should cook the sour cherries in advance: First, the cherries – rinse and pit them extensively, then cut them in half, sprinkle the sugar over them and let them juice for an hour. When the sour cherries have drawn juice, transfer them to a small saucepan and fill with enough water to just cover them. Bring to a boil and steep at a moderate temperature for 5 minutes, then cool. Pour the juice through a sieve and leave it open until it becomes a slightly thick cherry syrup, which you then pour repeatedly over the cherries. When this has cooled down repeatedly, you can finish cooking the fruit salad.
Remove the pits from the cherries, but whole. Cut the honeydew melon in half, scrape out the seeds with their lining, peel them off, and cut the flesh into cubes the size of the knapp cherries. Rinse the nectarines and cut them into large cubes on the spot. Toast the flaked almonds in a dry, heavy-bottomed frying pan over medium heat until golden, cool. Just before serving, mix everything together with the morello cherries – this is of course excellent with vanilla ice cream or simply semi-solid whipped cream with bourbon vanilla sugar.