Crust:
  1 cup graham cracker crumbs
  3 Tbsp. sugar
  3 Tbsp. butter, melted
 
 Filling:
  3 packages cream cheese (8 ounces each)
  1 cup sugar
  3 Tbsp. flour
  3 Tbsp. key lime juice
  1 Tbsp. grated lime peel *
  1/2 tsp. vanilla
  3 eggs
  1 white
 
 Topping:
  3/4 cup sugar
  2 Tbsp. cornstarch
  1/2 cup cold water
  1/2 cup key lime juice
  1 egg yolk
 Heat oven to 350F.
 
 Mix crumbs, sugar, and butter and press into bottom of a 9-inch springform
 pan.  Bake 10 minutes.
 
 Beat cream cheese, sugar, flour, juice, peel, and vanilla at medium until
 well blended.  Add the 3 whole eggs and the egg white, 1 at a time, mixing
 well after each addition. Pour over crust.
 
 Bake 40 minutes.  Turn off oven and let cake cool as the oven cools down.
 Loosen cake from rim of pan.  Cool completely before removing rim.
 
 Mix sugar and cornstarch in saucepan.  Gradually stir in water and juice.
 Bring to a boil over medium heat, stirring constantly.  Boil 1 minute until
 clear and thickened, stirring constantly.  Add small amount of hot mixture
 to slightly beaten egg yolk.  Return mixture to saucepan and cook 3 minutes,
 stirring constantly.  Cool slightly.
 
 Spoon topping over cheesecake and refrigerate at least 2 hours.
 
 Garnish with paper-thin slices of lime
 
 * I use regular lime peel and slices since I have no source for fresh key
   limes.  If you do, all the better.  I get the key lime juice from the King
   Arthur catalog.