Preheat oven to 325°F. Place an 8 x 8 pan on bottom rack and fill halfway with boiling water.
Spray a 9 inch springform pan with cooking spray. Wrap bottom of pan with aluminum foil, to prevent any leakage. Set aside.
In a medium-size mixing bowl toss together vanilla wafer crumbs with sugar and butter until fully moistened. Press onto bottom and halfway up sides of pan. Place pan into freezer while you make filing.
Using an electric mixer, whip together cream cheese, sugar and vanilla until completely smooth. Add cornstarch and vanilla, mixing well.
Add eggs one at a time mixing well after each addition. Scrape sides and bottom of bowl as needed. Mix in sour cream by hand.
Pour evenly into crust. Bake on middle rack of oven for 1 hr 10 - 1 hr 20 minutes or until the center is still slightly loose when gently shaken. It won't be completely set. Turn off oven, leave door slightly ajar, and leave cheesecake in oven for 1 hour longer to finish baking.
Remove to a cooling rack, and allow to cool for 30 minutes then run a knife gently around top edge. Cool completely to room temperature. Leave ring in place, wrap and chill for 1 preferably 24 hours.
To make the topping: In a small saucepan, whisk together brown sugar, syrup, cornstarch, eggs and salt. Gradually whisk in half and half. Turn heat to medium-high whisking constantly until thickened. Lower heat to a simmer and whisking constantly, cook for one minute.
Remove from heat, add butter and vanilla. Whisk until fully combined. Mix in pecans. Mix well. Set aside to cool for at least 20 minutes. Spread evenly on chilled cheesecake and return to fridge to set. Chill until serving.
Store leftovers chilled.