In a medium saucepan bring sugar, water and corn syrup to a boil. Once boiling, place a lid on pan for 2 minutes and then remove. The lid will trap steam which in turn will run down sides and take down any sugar crystals stuck to the side of pan. This is a very important step to prevent sugar mixture from turning grainy and crystallizing during boiling process.
Cook on high heat but if working on gas make sure that flames do not go up sides. Absolutely do not stir in pan as this will make syrup grainy!
When syrup has reached 245°F start whipping egg whites on medium speed in a stand mixer fitted with a whip attachment.
When syrup has reached 258°F remove from heat. Engage mixer in high speed. Pour syrup into whipping egg whites but make sure to pour it along inner wall of the bowl instead of pouring it towards middle of bowl.
At first mixture will be runny but will thicken and become thick meringue. After about 4 minutes remove a tablespoon amount and check to see if it holds it’s shape. If it does, stop mixing, otherwise mix slightly longer and retest.
Remove from machine and mix in vanilla and chopped pecans. Quickly pour into a baking dish that has been prepared with butter or non-stick cooking spray. Cool and cut into squares.