Preheat your oven to 350°F (175°C). In a medium bowl, mix graham cracker crumbs with melted unsalted butter until well combined. Firmly press the mixture into the bottom of a 9-inch springform pan, creating an even layer. Bake for 10 minutes or until lightly golden, then remove from the oven and allow to cool.

In a large mixing bowl, beat the softened cream cheese until smooth and creamy using a hand mixer on medium speed. Gradually add granulated sugar and cornstarch, mixing until fully incorporated. Add the room temperature eggs one at a time, followed by an extra egg yolk, mixing just until blended.

Reduce mixer speed to low and gently blend in the sour cream, freshly squeezed lemon juice, and vanilla extract until the mixture is smooth. Scrape down the sides of the bowl to ensure everything is well combined.

Pour the cheesecake filling into the cooled graham cracker crust, spreading it gently. Wrap the bottom of the springform pan in aluminum foil to prevent water from seeping in. Place the pan inside a larger roasting pan and fill the outer pan with hot water until it reaches halfway up the sides of the springform pan. Bake at 302°F (150°C) for about 30-45 minutes.

Once baked, turn off the oven, crack the door open, and allow the cheesecake to cool slowly for about an hour. After an hour, transfer the cheesecake to a wire rack to cool completely at room temperature. Cover and refrigerate overnight before serving.

After chilling, release the sides of the springform pan carefully. Slice your cheesecake into wedges and serve plain or topped with fresh berries or chocolate sauce.