Combine the chocolate, butter and Flamingo Estate Whole Bean Coffee espresso in a large bowl and place over a pot of simmering water. Stir occasionally until all is melted and combined. Set aside at room temperature.
Place egg yolks in the bowl of a stand mixer fitted with a whisk. Whisk on high speed until creamy. Meanwhile, place sugar and water in a small saucepan. Bring to a boil, stirring to dissolve the sugar. Continue boiling until the syrup reaches 250°F on a thermometer. With the whisk still running, stream the syrup into the egg yolks. Continue whisking for 5 minutes, or until the mixture is pale and very airy - it should triple in volume. Mix ¼ of the melted chocolate into the yolk mixture, then fold all of the yolk mixture into the chocolate mixture.
Thoroughly clean the mixer bowl and whisk. Add the egg whites and salt and whisk on medium speed until the whites reach soft peaks. Still whisking, stream in the sugar, then continue whisking to firm peaks. Fold the egg white into the chocolate/yolk mixture in three stages. Pour the mousse into serving bowls and chill in the fridge for at least four hours, or overnight.
Serve garnished with whipped cream, sea salt flakes, and a generous drizzle of Flamingo Estate Olive Oil.