The spoon sweets (in greek glyka toy koytalioy) have a long history in Greece. They are fruits which have undergone a treatment (completely natural) to become syrupy sweets. They are served in a small saucer with a small spoon.
The spoon sweets became very popular in Greece at the beginning of the last century (1910). It was then that they started to be served in traditional cafés as desserts or in order to accompany in a sweet way the Greek coffee. At that times, which was financially suffocating in Greece, the Greek households were making homemade spoon sweets and when there was a celebration in the house they were offering them to their guests for dessert.
Note, that the Greek climate favors the production of various fruits such as apples, peaches, pears, cherries, sour cherries, plums, apricots, figs, oranges, lemons, strawberries, pomegranates, quinces, grapes etc. and indeed they very tasty when they are fresh. (A small parenthesis here, if you like fruits you can enjoy them in Greece very much. You will be able to find them also in very good prices compared to other European north countries).
Thus, spoon sweets, are made from such fruits and sometimes vegetables (such as eggplant, pumpkin, etc.). In Thessaloniki, there are traditional type mini markets where you can find them. Some Greek taverns may also offer them to you for free after a meal. If you have not tried such type of sweet I surely recommend you to do so when you visit Thessaloniki.