This is a compound sentence.
A compound sentence contains at least two independent clauses. An independent clause is a clause that can exist on its own, unlike dependent clauses. In the sentence above, there are two independent clauses:
1. An éclair—a long, thin, frosted pastry—is traditionally filled with vanilla cream
2. (But) Its flavor can be enhanced with other fillings, such as chocolate, coffee, strawberry, or pistachio