As with making most candy, a good candy thermometer is essential. If the thermometer is off, you may not get the right results.
1 C sugar
16 TBSP butter (2 sticks)
1/4 C water
1/4 tsp salt
1 TBSP vanilla
1 C semi-sweet chocolate chips, melted
1 C pecans
Lightly butter a cookie sheet.
In a medium saucepan, melt the butter.
Add the sugar, water, salt, and vanilla and stir over medium-medium high heat with a heat resistant spoon or spatula until it comes to a boil. Make sure you are constantly stirring...burned candy is not good candy!
Clip your candy thermometer to the side of the pan and keep stirring until the thermometer reaches the hard crack stage (300 degrees F) and it is a golden brown color.
Pour the toffee onto the buttered pan and spread by tilting the pan or with a spatula into a thin layer.
Let it cool to room temperature. Blot with a paper towel if there are butter droplets on top.
Put the pecans in a food processor and process until crumbs are formed.
Spread the melted chocolate on top with a spatula.
Sprinkle with a layer of pecan crumbs.
Let the chocolate set completely.
Break into pieces and serve or store in an airtight container/bag.
Adapted slightly from http://www.melskitchencafe.com/