Crush 20 graham crackers (about 3 cups of crumbs) in a food processor or place them in a resealable bag and crush them with a rolling pin.
In a large bowl, combine 3 cups graham cracker crumbs and 2 tablespoons granulated sugar.
Stir in 12 tablespoons (1¼ sticks) melted unsalted butter until all the crumbs are evenly moistened.
Firmly press the crumb mixture into the bottom of a 9-inch springform pan.
Place the crust in the freezer while you prepare the cheesecake filling.
For the Cheesecake Layer:
In a large mixing bowl, beat 2 (8-ounce) blocks room temperature cream cheese and 1 cup sugar until smooth and fluffy.
Beat in 1 tablespoon cornstarch and ¼ teaspoon salt.
Add 1 teaspoon vanilla extract.
Add 3 eggs, one at a time, mixing just until incorporated after each addition.
Fold in ½ cup sour cream until smooth.
Pour the cheesecake filling over the chilled crust and smooth the top with a spatula.
Place the springform pan into a large roasting pan. Carefully pour enough boiling water into the roasting pan so it comes about halfway up the sides of the springform pan.
Bake for 30 minutes.
For the Pecan Pie Topping:
While the cheesecake layer is baking, prepare the pecan topping.
Combine the brown sugar, corn syrup, vanilla extract and butter in a medium sauce pan. Stir and bring the boil to a mixture and then heat for 2-3 minutes.
Remove the heat and allow the corn syrup mixture to cool.
In a separate bowl, whisk together 3 large eggs, ¼ teaspoon salt, and ¼ cup heavy cream.
Once the corn syrup mixture has cooled slightly, slowly whisk in the egg mixture until combined. Stir in 1 cup roughly chopped pecans.
After the cheesecake has baked for 30 minutes, carefully remove it from the oven and gently spoon the pecan topping evenly over the cheesecake.
Return the cheesecake to the oven and bake for an additional 40-50 minutes, or until the pecan topping is browned and the center of the cheesecake is just slightly jiggly.
Remove the cheesecake from the water bath and place it on a wire rack to cool completely.
Refrigerate for at least 4 hours, or overnight, before removing the springform pan, slicing, and serving.
Notes
This cheesecake can definitely be made ahead of time before serving. This cheesecake will keep in the refrigerator for up to 4 days.