In a food processor, blitz graham crackers, melted butter and sugars until well combined and resembles wet sand. Press into a spring form pan, its underside double wrapped in oversized, heavy duty aluminum foil.
Bake for 12-15 minutes, until it begins to brown and firm slightly. Remove and cool completely.
Lower oven to 325°
For the cheesecake filling, in a stand-up mixer with the paddle attachment, beat the cream cheese slightly to combine before adding the sugar and salt. Beat on medium until it becomes fluffy – about 2 minutes.
Add the lemon zest and cornstarch and beat until combined.
Add in the eggs, one at a time, allowing them each to become well incorporated before adding the next. After every other egg, or thereabouts, scrape the bottom and sides of the bowl with a rubber spatula.
Once all the eggs have been added, mix in the lemon juice and limoncello and beat until everything is completely combined but do not over-mix.
Pour the batter into the spring form. Lightly tap it against your counter to let any air bubbles come to the surface and pop.
Place the spring form in a roasting tray and pour in warm water – enough to come halfway up the spring form. Its easiest to use a tea kettle for this to help prevent water from splashing into the cheesecake – you so do not want that!
Bake the cheesecake for about 1hour 15 minutes to 1 hour 30 minutes, or until the cheesecake is firm but the center still has a slight wiggle to it. What you should see, when its still in the heated oven, is a cake that has not pulled away from the sides of the spring form and also has a slight wobble just below the surface of the cake. If it waves and shakes like Jell-O, its underdone, but a gentle sway, like the gentlest sign of a ripple, is perfect.
Turn the oven off and crack the door slightly. Allow the oven to cool completely before opening the door all the way and pulling out the over wrack and allow to cool one additional hour. If, by this point, the cake has begun to pull away from the sides of the pan that is totally fine. If it were to pull away from the sides while its baking that means the cake has overcooked, however, if it does so when the oven is off and the cake is cooling that’s not the case. That’s not say that if it hasn’t pulled away at all its underdone or anything—either way is fine—just be assured you’re on the right track. Remove from the water bath and move to the fridge to cool completely, at least 8 hours.
Your cream cheese and eggs MUST be room temperature, otherwise you'll never get the right texture. The best method is to just leave the cream cheese out on the counter (out of the box, but still in the foil package) for 4 - 6 hours. You can do the same with the eggs, or put them in a bowl of warm water for about an hour (just change the water out halfway through). And don't even think about microwaving the cream cheese! Now that it's summer don't leave the cream cheese out too long—it can get too soft and almost start to melt if your house is hot. You want it soft and spreadable but it should still hold its shape in the package when you pick it up.