This is a rich, magnificent dish, so enjoy it and don't even think about replacing the heavy cream with anything else or skimping on the amount. A sprinkle of lemon zest at the end gives it a bright pop.
This is an update to my last review. Made it this year with morels (as suggested) and it was NOT as good as last year's that I made with porcini mushrooms. I can't explain exactly why, but the porcinis imparted more flavor than the morels, and the flavor was more woodsy and mushroomy and pleasing. So my recommendation to all: use porcini mushrooms!
This is insanely good. It will be on our Thanksgiving table every year until wild mushrooms stop growing. I actually substituted porcini mushrooms for morel mushrooms (saving something like fifty bucks) and it was still off the charts delicious.