Generously butter the inside of a 10-inch spring form pan. Wrap a double layer of heavy-duty aluminum foil tightly around the outside bottom and sides, crimping and pleating the foil to make it conform to the pan. This will help to prevent water seeping into the pan when you put it into the bain-marie. Position the baking rack in the center of the oven; preheat the oven to 300* Fahrenheit.
In a large mixing bowl, using an electric mixer, beat the eggs with the sour cream until well blended.
In a medium-sized bowl, beat the cream cheese with the butter until smooth and creamy. Add this to the egg-sour cream mixture and beat until smooth.
Add the sugar, cornstarch, vanilla, lemon juice and lemon zest and beat thoroughly, about 2 minutes.
Pour into the prepared springform pan and place in a roasting pan (or other pan) large enough to prevent the sides from touching. Place in the oven and carefully pour in enough very hot tap water to reach halfway up the sides of the springform pan.
Bake for 2 hours, 15 minutes, or until the cake is very lightly colored and a knife inserted in the center emerges clean. Remove from the water bath and carefully peel the aluminum foil from around the pan. Let stand at room temperature until completely cool, about 4 hours. Refrigerate, covered, until well chilled. For best flavor and texture, this cheesecake is best chilled overnight.