A pastry that is purely vegetarian could be both kosher and halal. If a pastry contains lard, it is neither kosher nor halal. The use of carmine (red number 4), it is not kosher or hallal because carmine comes from a forbidden insect (cherry filling frequently has carmine die to make it an intense red). If a pastry contains ***, it might be kosher but it won't be hallal. If a butter-based pastry contains beef (for example, "pigs in a blanket" made with beef Hot Dogs), it could be hallel, but it is not kosher. (I say "could be" because both kosher and hallal certification are also concerned with the implements and oven used for baking, and with the provenance of the ingredients.)