Have all your ingredients measured and set out before you start the recipe.
In a heavy 2-quart saucepan, add sugar and butter.
Place the candy thermometer in the pan.
Melt the butter and sugar over medium-high heat, stirring constantly. Do not adjust the heat.
Stir mixture until the caramel turns an almond brown color and thermometer reaches 300ºF (hard-crack stage), about 20-25 minutes.
Immediately pour toffee mixture into one baking pan spreading an even layer to the desired thickness.
Sprinkle one cup of the grated chocolate over the toffee.
Allow the chocolate to sit for a minute or two; it will soften from the heat of the candy. Then, using a small spatula, spread over the toffee into a thin layer.
Sprinkle the nuts over the chocolate, as thick or as light as you desire. With your fingers, press lightly on the nuts to make sure they stick into the chocolate. Either greasing your hands or using a plastic bag as a "glove" will make this step easier.
Sprinkle lightly with the sea salt.
Place the baking pan in the refrigerator until set.
When set, remove the baking pan from the refrigerator and let it sit out until it reaches room temperature.
Place the other baking pan over the toffee pan and holding pans together firmly, flip the tray over. You are now ready to spread another layer of chocolate and nuts on that side.
Wipe the surface of the candy with a paper towel and allow to dry.
In a microwave, melt the remaining chocolate on 50% power for 2-3 minutes. Stir until all chocolate is completely melted. Time will vary depending on your microwave. Do not overcook.
Spread the melted chocolate onto the firm toffee and add the remaining nuts and salt, as in Step 9.
Refrigerate toffee until firm.
Remove the pan and then break the toffee into bite-size pieces.
Store in an airtight container in the refrigerator.