Heat 2/3 of the chocolate in the microwave or on the stove. If using a microwave, heat the chocolate in 30-second increments, stopping to stir vigorously each time. It should take 2 minutes or less to melt the chocolate. If using the stove, create a double boiler by filling a pot with a few inches of water then balance or hold a smaller pot filled with the chocolate just above the water line. As the water gently boils, the steam will melt the chocolate in the smaller pot without burning it. Stir occasionally, removing from heat as soon as the chocolate melts completely.
Remove the melted chocolate from the microwave or stove. Add the remaining hard chocolate to the hot melted chocolate, stirring vigorously until it melts as well.
Stir the macadamia nuts into the chocolate.
Line a rimmed dish of your choice with parchment paper or wax paper. The size of the dish will determine how thick the bark is. A 2-quart squarebaking dish makes thicker bark (like in the photos). A larger dish will obviously yield thinner bark.
Spread the chocolate evenly in the rimmed dish. Sprinkle with sea salt. Refrigerate for at least 10 minutes, longer if chocolate isn’t solid yet. Use a knife to cut the bark into squares or misshapen pieces. Store the bark at room temperature.