To make the sauce, stir together the crème fraiche, tarragon, and lemon zest. Let sit for 30 minutes to allow the flavors to blend.

To broil the salmon, place fish on a rack over a baking pan/broiler pan. Dot fish with butter, sprinkle with salt and pepper and layer on some lemon slices onto each. Pour wine into pan to about 1” depth (that should be enough so it won't all evaporate while the fish bakes). Broil in oven (approx. 10 min/inch, 3” from heating element), turning once if fillets are thick. Once flesh flakes easily with a fork, set aside to keep warm while finishing the sauce.

In a small skillet bring 1 cup of the white wine (use whatever is left from the broiler pan as well) to a boil. Once reduced by ½, whisk in the crème fraiche mixture. Stirring until mixture is warmed throughout.