In a saucepan, melt the butter. Stir in the flour and salt. Add the chicken broth all at once. Cook and stir until mixture is bubbly. Combine the egg yolks and lemon juice. Stir about half of the hot mixture, very slowly, into egg yolk mixture. Return this mixture to the remaining sauce in the pan. Cook and stir 2 minutes more. Makes about 1 1/2 cups sauce.