Preheat oven to 325 degrees F. Line inside of a 3x5 ½ inch petite loaf pan with non-stick foil or parchment paper. If making the shallower version, line two.
If using store-bought cookie dough rounds, press them into bottom of lined pan (or pans) and bake for 15 minutes. If using graham cracker/butter mixture, press into pan but don’t bake.
In a medium size bowl, beat cream cheese and sugar until well mixed. Add egg and egg yolk and stir until well mixed. Stir in lemon juice and vanilla. Pour this mixture over crust and place loaf pan (or pans) into a larger square pan.
Pour very warm water into the square pan so that it comes about halfway up sides of loaf pan. Bake on center rack of oven for about 38 minutes.
While cheesecake bakes, mix together sour cream, sugar and vanilla. Spread this mixture over top of cheesecake and return to oven for 5 minutes. Be careful not to overbake the sour cream topping. 5 minutes is all you need.
Remove from oven. Lift small pan from water and let cool on a cooling rack for about an hour. Transfer to refrigerator to chill for at least 3 or 4 hours.
Before serving, grasp foil and lift little cheesecake from loaf pan. Slice in half and plate.
Makes 2 servings (1 petite loaf pan) Each person gets half. If using two mini loaf pans, you'll have four smaller servings.