If using raw macadamia nuts, toast the nuts in a skillet over medium heat for 3 - 5 minutes, stirring frequently, until they are golden and smell nutty. Transfer to a bowl or dish and allow to cool.

In the same skillet, toast the unsweetened coconut flakes over medium low heat for 1 - 2 minutes, stirring frequently, until brown and fragrant. Transfer the coconut to the same bowl as the macadamia nuts and allow to cool

Line a baking sheet with a silicone mat or parchment paper and set aside.

In a medium saucepan, combine sugar, butter and water, cook over medium heat without stirring, only swirling the pan around to dissolve the sugar and to make sure the syrup brown evenly, until it turns a deep amber color, about 8 minutes.

Remove the saucepan from the heat. With a rubber spatula, stir in the toasted macadamia nuts and coconut set aside earlier to coat evenly. Add baking soda and salt and stir quickly to incorporate. This may bubble as the baking soda aerates the caramel, you should see a color change in the caramel.

Scrape the brittle out onto the prepared baking sheet and spread it out as thin as you can before it starts to harden.

Let the brittle cool completely. Break into pieces and enjoy.