Simple:
* The party decorations were made of ersatz gold, but they looked surprisingly realistic.
* He tried to make an ersatz coffee with instant granules, but it lacked the richness of the real thing.
More complex:
* The museum's collection of ersatz jewels, while not genuine, offered a fascinating insight into the history of imitation.
* In a world increasingly dominated by technology, some people yearn for a more authentic existence, rejecting the ersatz pleasures of the digital age.
* His attempt to create an ersatz family was doomed from the start, as he lacked the genuine connection he so desperately craved.
Note: "Ersatz" generally carries a negative connotation, implying something is artificial, inferior, or a substitute for the real thing.