Preheat oven to 325F.
Grease and flour an 8" or 9" springform pan
Pulse into fine crumbs:
1 C graham crackers (honestly this doesn't have to be exact; I usually just toss an entire single package of graham crackers into the blender).
Add in and pulse until totally blended:
3 tbsp sugar
3 tbsp butter
Pour into pan, press firmly until mixture covers entire bottom of pan.
Bake for ten to fifteen minutes, or until crust just barely starts to brown. Remove from oven. It's ok if it doesn't totally cool before you use it. Leave the oven on.
In a small saucepan on medium heat mix:
3/4 C sugar
1 tbsp lemon zest
2 large eggs
Cook until sugar is dissolved and the mixture turns a lighter colour (about three minutes)
2/3 C lemon juice
2 tbsp butter
Cook and stir with a wire whisk until mixture starts to thicken (5-10 minutes). If you put a spoon in the mixture and it comes out coated then it's done. If the mixture is still too liquid to stick then it needs to be cooked more. It should thicken as it cools. If you find that it doesn't thicken enough you can stick it back on the stove and cook it some more (I've had to do that, can you tell?) Set aside and cool.
In a separate bowl cream until totally smooth:
5 packages (8oz each) of room temperature cream cheese (temperature does matter!)
Add and mix until completely blended:
1 C sugar
1 tbsp lemon extract (optional but good)
3 tbsp flour
Add one at a time, blending between each one:
4 eggs that are at room temperature.
1 C sour cream (I use low fat).
Mix until sour cream is just blended.
Pour cheesecake layer on top of cooked crust. You can then do one of two things: either pour the lemon curd in circles on top and swirl it in artistically, or you can pour it all over in one separate layer. I've done both, they both work equally well. Bake cheesecake for 60-75 minutes, or until just set. (It should jiggle a little bit in the middle when you take it out, but not very much. It will set a bit as it cools). I tend to take it out, let it cool for about ten minutes and then run a knife around the edge; this can help prevent cracking. Then I let it cool to room temperature before sticking it in the fridge overnight.