Firstly, I normally freeze with a glass or metal bowl or a parchment layered tin, so once the final mixture hits the bowl it will be cold.
In a second bowl, lightly whip the cream. Set aside.
In a third bowl, place the egg yolk. using an electric whisk, beat the eggs to a light texture.
In a small saucepan, combine the sugar with the water. Place over medium heat and bring the syrup to the boil until it reaches the tread stage about 110–115°C (223–235°F), when a metal spoon is dipped in the last drops of syrup will form thin threads. or up to soft boil stage, 117-121˚C (242-250˚F). That means that when you drop a bit of it into cold water to cool it down, it will form a soft ball.
Remove the syrup from the heat. Using the food mixer in one hand and the syrup in the second hand, Slowly and steady whisk in the syrup onto the egg yolks so the egg yolk and syrup combine and create a sabayon. Continue to whisk until the sabayon sets and cools enough.
Fold the mixture into the cream and add the elderflower and vanilla extract.
Pour the mixture into the frozen container and place back in the freezer for a minimum of 1 hour or longer until set.
Cover and store for 2 months for best flavour.