Is it possible to replace the milk with buttermilk?

Just make sure to readjust your bakers ratio's due to you adding more fat to the recipe

It's true, Le Bec Fin, but in this case it's a non-issue, as yeast is the leavener.

but i do believe that bakers typically respond that changing from milk to buttermilk requires a change in your leavener(bak soda). I always forget the rule but you can find it through google.

Normally, I would say yes, but the recipe has you scalding the milk. If you try to scald buttermilk, it will separate into curds and whey, leaving you with a curdled, chunky mess. However, I still think you could use buttermilk--just don't heat it on the stove. Let it come to room temp and then add it. I mean, you could even use it cold, but it will slow the rising time.