Preheat oven to 350F. Toast the whole pecans on a cookie sheet for 6-8 minutes or until golden brown and fragrant. Remove, let cool slightly and then roughly chop.
Cover a large baking sheet with foil, making sure there is over hang on the sides. Spray with cooking spray and set aside.
In a heavy bottomed saucepot melt the butter, sugar, water and salt over medium heat. Stirring occasionally, cook until the mixture reaches 305F (hard-crack stage). Remove from heat and stir in the vanilla and chopped pecans.
Quickly pour the mixture onto the prepared cookie sheet using a spatula flatten into an even layer. Cool for 30-40 minutes or until set.
In a double boiler, gently melt the chocolate making sure not to scortch it. Pour the chocolate over the hardened toffee, covering fully. Let set for 5 minutes and then sprinkle liberally with the salt.
Let cool, at room temperature for 1 hour or until the chocolate has hardened. Break into medium sized pieces. Store in an airtight container for up to 1 month.
Recipe Courtesy of Megan Mitchell