Whisk egg yolks until blended; whisk in Key lime juice. Add condensed milk, vanilla, and salt, whisking until blended.
Pour mixture into crust. Bake at 350° for 15 minutes.
Remove from oven; cool completely on a wire rack. Chill until ready to serve. Garnish, if desired.
Note: For pies with more filling, triple the filling ingredients, and divide evenly between 2 graham cracker crusts.