Butter a 9×13 in pan.

In a 3-quart heavy-bottomed sauce pan over medium heat, melt the two sticks of butter.

Once the butter melts, add the sugar, the corn syrup, and the water. Stir and insert a candy thermometer.

Continue to cook over medium heat (a low-rolling boil), stirring occasionally, until the temperature reaches 300°F.

Once the liquid reaches 300°F, quickly add the macadamia halves, stir rapidly, and pour the candy out into the prepared pan.

Let the toffee cool completely (about 30 minutes), then turn out from the pan and wipe off any excess butter.

In a medium-sized microwave-safe bowl, melt the chocolate on 50% power.

Spread the chocolate over the toffee, sprinkle the chopped macadamias into the chocolate and press them down.

Once cooled, break the toffee into pieces and store in the refrigerator in an airtight container.