President Abraham Lincoln was no stranger to this delicious treat. In fact, lemon custard pie as made by Nancy Breedlove was one of his favorite treats. Mrs. Breedlove kept a hotel in Illinois in the mid-1800s, and
Lincoln stayed there for weeks at a time when involved in court trials. He liked her lemon custard pie so much that he requested that she write out the recipe for him, and he told her years later that it was the favorite White House dessert, used by the chefs in the Presidential home.
 
Apparently in 1913, Mrs. Breedlove, then 80, hosted a “Lincoln party” at her home in Owossa, Michigan to celebrate the 50th anniversary of the Gettysburg address. Her Lemon Custard pie was the main feature of the menu. Here is her recipe:
 
Abraham Lincoln’s Lemon-Custard Pie
Two-thirds of a cup of water, one teacup of sugar, the yolks of three or four eggs; grated rind and juice of one lemon; one tablespoon of cornstarch; fill a pie shell and bake in a hot oven. Beat up the whites of the eggs separately to a stiff froth, mix in three tablespoonful of sugar and spread over pie. Bake to a nice brown. 

Sources: Mrs. Goodfellow: The Story of America's First Cooking School; "Abraham Lincoln's Lemon Custard Pie," The Tacoma Times, 19 Nov 1913, Wed, First Edition