Pour 1cm water into a frypan and bring to a simmer.
In an electric mixer bowl combine sugar, egg whites and water. Put the bowl in the frypan of simmering water and whisk gently until mixture is 70 degrees C (check with a thermometer). Move the bowl to the mixer and whisk at medium high speed until it forms stiff peaks, about 5 minutes.
Reduce speed and beat in the butter, one tablespoon at a time. Beat in the vanilla extract, orange extract and Grand Marnier until smooth.