Bring Me Their Hearts by Sara Wolf

Zera is a Heartless – the immortal, unageing soldier of a witch. Bound to the witch Nightsinger ever since she saved her from the bandits who murdered her family, Zera longs for freedom. With her heart in a jar under Nightsinger’s control, she serves the witch unquestioningly. Until Nightsinger asks Zera for a Prince’s heart in exchange for her own.

Crown Prince Lucien d’Malvane hates the royal court as much as it loves him – every tutor too afraid to correct him and every girl jockeying for a place at his side. No one can challenge him – until the arrival of Lady Zera. She’s inelegant, smart-mouthed, & out for his blood.

So begins a game of cat and mouse between a girl with nothing to lose and a boy who has it all. Winner takes the loser’s heart. Literally.