Complex sentence: They can be found in almost every pastry shop in the country, as well as in Chile, Uruguay and Argentina where it's not only filled with custard (called "Crema pastelera"), but with jam (specially red ones) or manjar blanco.
Split into simpler sentences: They can be found in almost every pastry shop in the country. Such versions are also found in Latin America, in Chile, Uruguay and Argentina, where it's not only filled with custard (called "Crema pastelera"), but with jam (specially red ones) or manjar blanco.