When ready to bake cheesecake, preheat oven to 325 degrees F.

In a bowl, combine cracker crumbs and butter. Firmly press onto the bottom and up the sides of a 9 inch pie plate. (If using a deep dish, like a pyrex, bring crust up to just to the bottom of the ridges.) Cover and refrigerate for 30 minutes. (See instructions to bake crust if desired, below.)

In a large bowl, beat the cream cheese and sugar just until smooth. Add eggs, one at a time, beating on low after each until just until combined. On the lowest setting, add in vanilla and lemon zest and beat just until blended.

Pour into prepared crust and bake for about 25 minutes or until almost completely set; the very center, about 2 inches or so, should still have just a little bit of a wobble when the pan is gently shaken. Remove from the oven; let stand for 5 minutes while you prepare the topping, leaving oven on.

Combine the sour cream, sugar, and vanilla; it should be a thick pourable consistency, if not, add milk by the tablespoon until it is. (Should be able to pour while nudging with a spatula, about the consistency of a thick pancake batter.) Pour and spread carefully over the cheesecake.

Return cheesecake to oven and bake an additional five to seven minutes longer, until topping looks just “set”. The topping should still be pure white; don’t brown it or allow it to pick up any color. Cool on a wire rack for an hour and refrigerate eight hours or overnight before serving.

To bake the crust:

Preheat oven to 350 degrees F. Bake for 6 to 8 minutes, then cool before filling.