The proof was in the pudding.

An elderly Long Island husband and wife were busted yesterday for tampering with boxes of Jell-O pudding — replacing the contents with sand and salt and then returning them to stores for the $1.40-a-pop refund, officials said.

Alexander Clement, 68, and his wife, Christine Clement, 64, of East Northport disposed of the evidence afterward — by cooking up and eating the contents of the boxes they had emptied, authorities said.

Their puddings of choice? Pistachio and butterscotch.

Police said the couple struck four stores a total of five times. Christine would buy about 10 boxes each time. Her hubby was the driver.

When the pair got home, she allegedly would empty the boxes’ contents and replace them with plastic sandwich bags filled with the sand and salt.

After resealing the boxes, her husband would drive her back to the stores, where she would return them for a refund, police said.

The scheme fell apart after a customer who bought one of the resealed boxes complained. Police traced the boxes back to the Clements.

But authorities said the couple — who are well-off and have been married 40 years — is more to be pitied. Christine Clement is suffering from “an age-related mental issue,” police said.

“This was a bizarre story to begin with, and it just got worse when we found out what happened. It’s sad,” said Suffolk Police Lt. Michael Murphy.

“These aren’t bad people. They never had any problems before. It was a complete aberration. They are very apologetic.”

selim.algar@nypost.com

