We ask your eminence about working in a pastry shop that sells tarts?

It is permissible to sell tarts (cakes) and work in shops that sell them, as long as they are made from permissible ingredients. However, if the seller knows that the buyer will use it for a forbidden celebration, such as birthdays or Christmas, then it is not permissible to sell it to him, due to the generality of Allah's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression," and due to Imam Ahmad's ruling on the prohibition of selling anything that aids in sin.