How to Make It
Sprinkle gelatin in cold water in a small bowl. Stir and let stand 10 minutes.
Meanwhile, whisk together yogurt, macadamia extract, and 1 1/2 cups of the cream in a large bowl. Heat sugar and remaining 1 1/2 cups cream in a small saucepan over medium; bring to a simmer, stirring until dissolved. Remove from heat; stir softened gelatin into hot cream mixture until dissolved. Pour hot cream-gelatin mixture and 3 tablespoons of the rum into yogurt mixture, and stir until blended. Divide custard among 8 (4-ounce) ramekins, and chill, uncovered, until thoroughly chilled, about 30 minutes. Cover with plastic wrap, and chill 8 hours or overnight.
Heat caramel sauce with remaining 2 teaspoons rum in a small saucepan over low until warm, about 1 minute. Cool slightly, and spoon a thin layer of caramel rum sauce on each custard; sprinkle with fleur de sel, and serve.