1. Place the verjus and the chopped shallots in an 8- to 10-inch frying pan over high heat. Add the salmon steaks. Cover and bring to a simmer. Reduce the heat and simmer until the fish is no longer translucent in the center, 4 to 5 minutes.
2. Lift the fish onto 2 dinner plates and keep warm. Strain the juices and return to the pan. Boil juices over high heat until they have been reduced to 1/3 cup, 5 to 7 minutes, then whisk in the butter. Pour over the fish.