Chop the macadamia nuts roughly.

In a food processor, pulse the macadamia nuts, graham crackers, and brown sugar together until broken down to a sandy texture.

Stream in melted butter and pulse until the crumbs start to clump together.

Press into a 9-inch pie dish until it is compact.

Cover and place in the refrigerator until ready to use.

In a small bowl, mix the gelatin and the water. Set aside.

In a large heat-safe bowl, whisk the egg yolks until lighter in color.

Add the salt, half the sugar, and half the guava concentrate. Whisk thoroughly.

Place the mixture over a double boiler and cook. Stir constantly until smooth and slightly thickened.

Add the thickened gelatin mixture and whisk thoroughly while still on the double boiler until no lumps remain. Then, remove from the heat and cool to room temperature.

Once cooled, add the lemon juice and remaining guava concentrate. Chill in the refrigerator until the mixture partially sets.

In a separate medium-sized bowl, beat the egg whites with the remaining sugar until soft peaks form.

Fold the half of egg whites into the partially set guava mixture until just combined. Then, gently fold in the second half of the egg whites.

Pour into the chilled pie crust, smooth the top, and chill for at least 1 hour.

Optional: just before serving, top with whipped cream and chopped macadamia nuts.