Put 6 of the best looking mushroom caps aside. Slice the rest of the mushrooms along with the shallots, and carrots. Saute veggies in 2 TBS butter over medium heat until soft. (About 5 minutes). Add champagne and chicken broth and bring to a boil. Add mushroom tops and continue to boil for 3 minutes.
Mix together the ½ cup butter and ¼ cup GF flour and whisk into the veggie mix to thicken. Simmer until the sauce is thick and bubbly (Usually about 2-3 minutes). Then stir in the heavy cream and 2 TBS lemon juice, heat for 1 minute more, then remove from the stovetop.
Lay out on one or two cookie sheets 4 parchment papers measuring 12″ x 12″. Lay ½ lb. of fish on each one. Pour ¼ cup of sauce over the top of each fish. There will be extra sauce to use later. Roll down the parchment paper at the top leaving a small space above the fish, and then fold the ends underneath the fish to be sure it is sealed. Bake in a 400 degree oven for 20 minutes.
You can serve this on a plate where people open the paper at the table or slide the fish and sauce onto the plate just before serving. Serve the extra sauce on the side. Is delicious served with steamed green beans. Enjoy!
If the parchment paper seems a little overwhelming, you can replace it and use aluminum foil instead.