In a food processor, reduce the Nilla wafers to fine crumbs and transfer to a large mixing bowl. Chop the pecans fine and add them to the bowl. Set aside.
Melt the chocolate in a heatproof bowl set over a pot of over hot, but not boiling water. Stir in the sugar, corn syrup, and bourbon. Add this mixture to the crumb mixture. Blend by hand until well combined.
Form tablespoon-sized lumps of the mixture unto balls, rolling between the palms of your hands. Drop the balls in a bowl of sugar and toss to coat. Transfer to an airtight container, arranging the balls in single layers separated by parchment. Store the bourbon balls tightly sealed at room temperature. They get better (mellower, and with a smoother texture) as they age.