Preheat oven to 450 degrees.
Melt butter and olive oil in heavy bottomed saut pan over medium heat. Season cod with salt and pepper. When butter froths, add cod, presentation side down. After 2-3 minutes, put fish in a 450 degree oven (do not flip fish). When fish is done (5-10 minutes depending on thickness), remove from pan and flip onto paper towel to rest.
Return pan to stove, add a pat of butter and chanterelle mushrooms, saut for 2-3 minutes. Add shallots and saut for 2-3 more minutes. De-glaze pan with sherry and ignite to flame. Add chicken stock and reduce until it coats the back of a spoon. Add cream and season with salt and pepper.
To Serve:* from the Foley Fish Cookbook
Place cod browned side up on top of mashed potatoes. Spoon chanterelle mushrooms and sauce around the outside of the plate. Garnish with chives. Chef Chris Kuhn, Sherwood Inn, Skaenateles, NY