In a large bowl beat the cream cheese until soft (at least 2 minutes). Turn off the mixer and scrape down the sides of the bowl as you go.
Beat in the sugar. Then mix in the cornstarch (you may need to sift it first), lemon juice and vanilla extract.
Mix in the sour cream, continuing to scrape down the sides of the bowl as necessary.
With the mixer on low speed, mix in the eggs 1 at a time. Only mix the batter until the eggs look just combined. You can turn off the mixer and gently fold them in with a rubber spatula.
Place the spring form pan (wrapped in aluminium) inside a large roasting pan.
Pour the cheesecake batter into the pan.
Then pour water into the roasting pan so that there's about ½-1 inch of water.
Place the roasting pan (with cheesecake inside) into the oven. Bake for 40-50 minutes or until the top looks almost set except for in the very middle and there's a little wobble still in the middle of the cake.