The Rules of Gentility by Janet Mullany
Regency heiress Philomena Wellesley-Clegg has rather strong opinions about men and clothing. As to the former, so far two lords, a viscount, and a mad poet have fallen far short of her expectations. But she is about to meet Inigo Linsley, an unshaven, wickedly handsome man with a scandalous secret. He's nothing she ever dreamed she'd want -- why then can she not stop thinking about how he looks in his breeches?