How to make the sour cream that some restaurants serve with quesadillas?
There are many variants of sour cream. I am not quite up to date on the naming of dairy products in Belgium, but don't you find sour cream labeled as "zure room" (Dutch) or "crème aigre" (French)?

Mexican sour cream (Crema Mexicana) has however a higher fat content than the sour cream commonly available in European countries. A close approach is crème fraîche, but it might not be just as sour. If you want to make it yourself, you can add living bacteria culture (e.g. from yogurt) to heavy cream (fresh cream with >35% fat) and keep it at roughly 37°C until it reaches the required thickness.