Duke the Halls by Felicity Niven

The Duke of Kittredge is that rarest of men—a wealthy, tall, and still-unmarried duke at the age of thirty-one. As such, he’s perennially at the top of the “Most Eligible Bachelor” list of the ton. And yet, he’s never gotten close to landing a wife. Young ladies don’t seem to like him. Scratch that. They revile him. And he’s in complete sympathy with their opinion of him.
Because he is, without question, an insufferable clodpole.
But to please his mother, he’s promised to attend a Christmas country house party where he will meet a dozen possible future duchesses. He will waltz and carol and stand under mistletoe when all he really wants to do is cloister himself in his London library with a fire, a stack of books, and his dog.
So he does what any rational, right-thinking duke would do.
He runs away.

Enter Franny Cranwell, ray of sunshine. After what they’ve both been through, Franny just wants her little brother Ren to have the best Christmas ever. And he will. She’ll make sure of it. And if that means she has to give an adorably grumpy duke lessons in how to speak, act like a human being, and win a wife, she’ll do that.
If only the darling duke weren’t so handsome and so brooding and so unintentionally funny.
And such a good kisser.