However, here are some playful options you could use:
* A crumble of tarts (referencing the pastry base)
* A sweetness of tarts (referencing the sugary filling)
* A confection of tarts (referencing the overall nature of the baked good)
* A temptation of tarts (referencing the allure of the treat)
Ultimately, the best collective noun depends on the context and the specific type of tarts you are referring to.