Use either a pre made pie crust from the freezer section of your local market or make your own pie crust and blind bake for about 10 minutes in a 425 degree oven.
See below for some great tips on how to blind bake.
In a medium sized bowl, whip the egg whites to stiff peaks and set aside.
Using a mixer, cream the butter well then add the sugar. Continue to cream until light and fluffy. Add the egg yolks and continue to mix. Slowly add the buttermilk followed by the lemon juice then zest.
It's now time to incorporate the egg whites by folding them into the creamed mixture.
Pour into your prepared pie shell. Bake at 350 degrees for about 50 minutes or until the pie is set. The top will be a golden brown color. Cool on a wire rack and serve slightly warm or at room temperature.