Restaurant Piet de Leeuw (since 1946) has always been known for its good steaks.
But it really became well-known after an investigation by the Amsterdam newspaper Het Parool, which showed that the steak they sold wasn't cow meat but horse meat. At first, the owner denied he sold horse meat, but later he admitted Het Parool was right. And that they had been selling horse meat since 1946.
Nowadays, they are open about this on the menu, where you may find cow and horse steak.
Piet de Leeuw restaurant