Preheat oven to 450 degrees F.
Clean and gut fish, remove top and bottom fins, scale and remove gills. Whisk egg whites to soft peaks and fold in salt. Place thyme in body cavity and set aside. Place 4 tablespoons of egg white mixture on a large platter, suitable for oven to table use. Place fish on top of mixture and spoon remaining mixture over top of fish. Place fish and platter in oven and bake for 25 to 30 minutes. remove and strike crust to crack. Carefully remove salt crust from top of fish and divide flesh among two plates. Serve with good oil and lemons.
(An excellent accompaniment would be an arugula and tomato salad.)