The raising agent. A pastry (patisserie) is a small cake or tart, usually made with baking powder. Bread pastry (viennoiserie) such as croissants or pains au chocolat is raised with yeast.
Pastry is supposed to be crumbly! Just kind of squish it...But, if it's cooked, crumbly, and just not working, you would have to moisten it...Try (just a really small smidgen at a time) water!