"They're the Chocolate Cauldrons Romilda gave me before Christmas and they're all spiked with love potion!'
-- Harry Potter
Chocolate Cauldrons are cauldron-shaped chocolates that are filled with Firewhisky (HBP15).
Romilda Vane gives Harry a box of them just before Christmas in 1996. She had laced them with a love potion hoping that Harry would eat them, fall in love with her and take her to the Slug Club Christmas Party. Luckily for Harry, Hermione overhears Romilda planning this and warns him (HBP15).
On his 17th birthday, Ron mistakenly eats the chocolate cauldrons thinking they were a birthday present and his falls madly in love with Romilda until Professor Slughorn brews an antidote for him (HBP18).
"'Well, just be careful what you drink, because Romilda Vane looked like she meant business,' said Hermione grimly" (HBP15).
"'Well, take these anyways,' said Romilda, thrusting a box into his hands. 'Chocolate Cauldrons, they've got Firewhisky in them. My gran sent them to me, but I don't like them.' 'Oh, - right - thanks a lot,' said Harry, who could not think what else to say" (HBP15).