The Queen star admits she wasn't always a fan of the late November (12) break as it reminded her too much of Christmas back home - but now she lives in the U.S. with her moviemaker husband Taylor Hackford, she has adopted his favourite day of the year as one of her own.
She says, ""I didn't really like Thanksgiving when I first came here because, for me, it kind of interfered with Christmas; it was like Christmas but without presents.
""And also you ate turkey, and for us in England, you had to wait 'til Christmas to eat your turkey.""
Mirren reveals she's in charge of the gravy for the annual feast and she always looks forward to Hackford's traditional family treat.
She adds, ""I'm in charge of the gravy and my husband makes this thing called dressing... It sits outside the turkey and it takes three days to make... One day of which is me going out shopping, looking for buttermilk... They've (supermarkets) always run out.
""It's his mother's mother's recipe and it's a tradition in our family... He makes cornbread first... you chop, like, a ton of celery and onions and he makes huge pans. It lasts to the next Thanksgiving.""