Preheat the oven to 160° C fan.
Oil the square baking tin.
Mix the milk & eggs w/ an egg whisk or w/ your handheld electric mixer. Then add sugar, vanilla sugar & salt; finally incorporate the flour. (Use the electric mixer at this step to avoid lumps.)
Drain the morello cherries.
Add about ¼ of the dough to the tart form & bake for about 5 min.
Add the morello cherries & the rest of the dough; bake for about 45 min.
Dust w/ icing sugar.