Lay sheets of waxed paper onto two cooling racks and set aside.
Heat the sugar, corn syrup and water over medium heat in a heavy bottomed saucepan. Using a candy thermometer, heat the mixture until it reaches 250º F, a hard ball stage.
As the syrup is cooking, whip egg whites, along with a pinch of salt, until stiff peaks have formed.
When the sugar syrup has reached hard ball stage (250º F), remove it from the heat and begin to slowly pour it into the beaten egg whites, whipping together at a high speed.
Add the vanilla and continue whipping the mixture on high until it holds its shape and does not fall back onto itself, about 5-6 minutes. Stir in chopped pecans, if using.
Using two teaspoons and working quickly, drop scoops of divinity onto sheets of waxed paper that has been placed on top of cooling racks. If the divinity begins to harden, add a few drops of warm water to help loosen it while working.
Allow the divinity to dry and harden. This usually takes a couple of hours to overnight. Store in an airtight container for up to two weeks.