Preheat the oven to 350 degrees F. Grease and flour 2 baking sheets with 2 tablespoons butter and 2 tablespoons of flour. Mark parallel lines in the flour across the width of the tray about 4 inches apart. Put the eggs and sugar in a large mixing bowl, and with an electric mixer fitted with a wire whisk beat on medium-high speed until the mixture is pale yellow, thick, and has tripled in volume, about 8 minutes, using the mixer. Add the egg whites, remaining 3/4 cup flour, salt and vanilla, fold to mix thoroughly so the mixture is smooth. Fill a large pastry bag with a 3/4-inch plain tube with the mixture. Pipe fingers about 4 1/2-inches in length on to the baking sheet, using the lines as a guide. Dust the ladyfingers with powdered sugar. Bake until for 15 to 18 minutes, or until just firm on the outside and soft in the center.
Recipe adapted from LaVarenne Practique Cookbook, by Anne Willan, published by Crown