Three Promises Before Christmas by Tanya Wilde

This novella was previously part of the Kisses and Winter Wishes anthology.
When Caroline Harwood, illegitimate daughter of Baron Digby, met Mason Flowerdy, the Honorable Viscount Lonsdale, she felt only a faint pinch of guilt at what she was about to do—steal his pocket watch.

She never imagined:
– She’d get caught
– The viscount to be the most shameless man alive
– Fall utterly, hopelessly, and most inappropriately in love with her target