Millionaire Under the Mistletoe by Tessa Radley

Callum Ironstone didn't do guilt. Even so, the millionaire did feel responsible enough for struggling chef Miranda Owen to offer her a job. She could cater his holiday dinner party...an important affair where he planned to propose to the appropriate woman. Except somehow he'd ended up with Miranda in his bed.

He tried to blame it on the mistletoe. But Callum knew Miranda's transformation from dowdy wallflower to sensual beauty had hit him right where it counted. Perhaps she could be made into the hostess his position demanded...provided Miranda forgave him for destroying her family.