1) Meanwhile, combine the granulated sugar, golden syrup, salt, and 120ml water in a small saucepan and cook over medium heat until the granulated sugar dissolves. Raise the heat to high and cook until the syrup reaches 115°C on a candy thermometer. Remove from the heat.
2) With the mixer on low speed, slowly pour the golden syrup into the dissolved gelatine. Put the mixer on high speed and whip until the mixture is very thick, about 15 minutes. Add the vanilla and mix thoroughly. For the topping: 1) Sprinkle half the toasted coconut in a 20x30cm non-metal pan. Pour in the marshmallow batter and smooth the top of the mixture with damp hands. Sprinkle on the remaining toasted coconut. Allow to dry uncovered at room temperature overnight.
2) Remove the marshmallows from the pan and cut into squares. Roll the sides of each piece carefully in icing sugar. Store uncovered at room temperature.