Melt butter in sauce pan over medium-low heat. Once butter is melted, stir in sugar until combined. If using a separate candy thermometer, place thermometer into pan - attach to the edge of the pan if able but don't let the thermometer base touch the bottom of the pan.

On medium heat, continue to heat and stir mixture until it reaches the ‘hard crack’ stage (between 305-310 degrees Fahrenheit). The mixture may appear to separate and almost look curdled as it comes up to temperature; as long as you don't heat it over 310 degrees and continue stirring it should come back together.

Once the mixture is at temperature, pour quickly out onto the baking sheet covered with parchment paper or a silicone baking mat. Allow to cool to room temperature, until set.

Melt semisweet chocolate in microwave (on half power in 30-second intervals) or in a double-boiler. Spread over toffee. surface with an offset spatula. Before chocolate sets, spread chopped pecans over the top and press them gently into the chocolate.

Once the chocolate has set, break apart the toffee into bite-sized pieces – this can be done with a knife, but I like the shapes I get breaking it with my hands better!

As the mixture gets close to temperature, you may notice it start to ‘split’ with butter coming apart from the toffee mixture. It should come together when the mixture gets to the ‘hard crack’ temperature. I had it split when I didn’t get it hot enough AND when I over-heated it – make sure your thermometer isn’t touching the base of the pan and stir until you reach your goal temperature!